How do Sola Scriptura defenders have a list of "scripture" since the list isn't mentioned in scripture?

This is a good question. As mentioned elsewhere, Sola Scriptura is only the belief that scripture is the sole source of Christian faith and practice. What SS does not do is provide a list of books, although at the time of the Reformation, everyone agreed on at least the 66 books and definitely the books of the New Testament.

The doctrine of Sola Scriptura, in a nutshell, affirms that Scripture is our only source of normative, apostolic, infallible revelation and that “all things necessary for salvation and about faith and life are taught in the Bible with sufficient clarity so that the ordinary believer can find it there and understand it.” -source-

So, where is the "table of contents" for the Bible? Some believe the Catholic Church at Trent defined the contents. Others believe Christ delineated the table of contents.

Here is Irenaeus on the four gospels.

8. It is not possible that the Gospels can be either more or fewer in number than they are. For, since there are four zones of the world in which we live, and four principal winds,3449 while the Church is scattered throughout all the world, and the “pillar and ground”3450 of the Church is the Gospel and the spirit of life; it is fitting that she should have four pillars, breathing out immortality on every side, and vivifying men afresh. From which fact, it is evident that the Word, the Artificer of all, He that sitteth upon the cherubim, and contains all things, He who was manifested to men, has given us the Gospel under four aspects, but bound together by one Spirit. As also David says, when entreating His manifestation, “Thou that sittest between the cherubim, shine forth.”3451 For the cherubim, too, were four-faced, and their faces were images of the dispensation of the Son of God. For, [as the Scripture] says, “The first living creature was like a lion,”3452 symbolizing His effectual working, His leadership, and royal power; the second [living creature] was like a calf, signifying [His] sacrificial and sacerdotal order; but “the third had, as it were, the face as of a man,”—an evident description of His advent as a human being; “the fourth was like a flying eagle,” pointing out the gift of the Spirit hovering with His wings over the Church. And therefore the Gospels are in accord with these things, among which Christ Jesus is seated. Irenaeus

Further, he makes it clear that the scripture was handed down as already divine.

1. We have learned from none others the plan of our salvation, than from those through whom the Gospel has come down to us, which they did at one time proclaim in public, and, at a later period, by the will of God, handed down to us in the Scriptures, to be the ground and pillar of our faith. -ibid-

And here is Athanasius with the same idea that scripture was already handed down as divine from the beginning.

3. In proceeding to make mention of these things, I shall adopt, to commend my undertaking, the pattern of Luke the Evangelist, saying on my own account: ‘Forasmuch as some have taken in hand4543,’ to reduce into order for themselves the books termed apocryphal, and to mix them up with the divinely inspired Scripture, concerning which we have been fully persuaded, as they who from the beginning were eyewitnesses and ministers of the Word, delivered to the fathers; it seemed 552good to me also, having been urged thereto by true brethren, and having learned from the beginning, to set before you the books included in the Canon, and handed down, and accredited as Divine; to the end that any one who has fallen into error may condemn those who have led him astray; and that he who has continued stedfast in purity may again rejoice, having these things brought to his remembrance. -39th Festal Letter-

There is much more to the idea that scripture accredited itself, written as it were by eyewitnesses or companions between the bookends of James and John Sons of Zebedee, first and last apostles to die.

First of all, thanks for referring back to your own post, where you write:

But I have this question. Since all of the biblical texts provided for scripture were written PRIOR to the canonization of the New Testament, how could they possibly be referring to the 66-book Protestant Canon? Isn’t it more likely that these verses are referring to the Jewish Pentateuch or the OT?

This provides me with some vital context.

Thanks also for striving to provide some structure and substance to what sola scriptura means. For my own part, I've provided some useful considerations about that phrase here

As one begins to become acquainted with 'canonical studies', you quickly realize that there are a number of ways scholars approach answering the question, "what is included in the canon." And they roughly follow a chronological path:

1. What do the authors of the Bible books say about themselves and each other
2. How were these books used publicly (authoritatively read in public worship)
3. When/how were they gathered into collections (manuscripts such as the great uncials, Vaticanus, Sinaiticus, Alexandrines, and papyri like the Chester Beatty collection (P45, P46))
4. When/how were they collected in lists (Muratorian fragment, Athanasias' festal letter, etc)

As best as I can understand it, your question is about stage 1. My answer is going to focus in on that 'stage' and will be somewhat brief (hopefully):

How do authors speak about themselves?

An example of this would be Paul, as he opens his letter to the Galatians:

Παῦλος ἀπόστολος οὐκ ἀπ’ ἀνθρώπων οὐδὲ δι’ ἀνθρώπου ἀλλὰ διὰ Ἰησοῦ Χριστοῦ ⸋καὶ θεοῦ πατρὸς⸌ τοῦ ἐγείραντος αὐτὸν ἐκ νεκρῶν, (Gal. 1:1 NA28-T)
Paul, apostle not from people, nor through people, but through Jesus Christ and God, the Father who raised him from the dead..."

The context here is significant. Since his authority was contested, he provides his authority to speak/preach/write as an apostle. In other letters he just writes (since they weren't contesting that right)

How do authors speak about others?

This is just as interesting of a question. Let's look at a few examples from Paul:

λέγει γὰρ ἡ γραφή· ⸂βοῦν ἀλοῶντα οὐ φιμώσεις⸃, καί· ἄξιος ὁ ἐργάτης ⸄τοῦ μισθοῦ⸅ αὐτοῦ. (1 Tim. 5:18 NA28-T)
For scripture says, 'do not muzzle an ox while it is treading out the grain'and, 'a worker is worth his wages.'

⸂ἐν γὰρ τῷ Μωϋσέως νόμῳ γέγραπται⸃· οὐ ⸀κημώσεις βοῦν ἀλοῶντα. μὴ τῶν βοῶν μέλει τῷ θεῷ (1 Cor. 9:9 NA28-T)
for it is written in the law of Moses, 'you will never muzzle an ox while it is treading out the grain.' God's concern is not about oxen, is it?

The first detail we note is that Paul references Moses both as authoritative and also as a collection.

The second detail we note is that Paul treats Luke's gospel (where Jesus speaks these words (Lk 10:7)) as just as authoritative as Moses.

So, already, we have NT authors quoting and treating each other as authoritative.

So, on the one hand, it is very true to assert that we do not have a list at stage one (up to about 200 AD). But, on the other hand, it's clear that they had collections even at that early stage.

I'm trying to be very narrow in my answer, because, from how I read your post, you are trying to be very narrow in your question. And I hope that my narrowness of an answer hasn't excluded some of the context in which you are asking your question.

Scripture is not read in a vacuum.

Words are not read upon a page, without any other input from heaven.

when he, the Spirit of truth, is come, he will guide you into all truth: [John 16:13, KJV]

Without the indwelling Spirit, one is bereft. What is truth ? What is true ? What is not ? . . . . are questions one cannot answer alone. One needs the indwelling Spirit of God, a witness within, a hidden wisdom.

My sheep hear my voice, and I know them, and they follow me: [John 10 : 27, KJV]

Jesus Christ, himself, knows his own. And he speaks (yes, through the word, but also within, in Spirit).

And they hear.

And they follow him.

And a stranger will they not follow, but will flee from him: for they know not the voice of strangers. [John 10:5, KJV]

But other voices, other words, abound.

Yet they hear nothing of his tones, in those words.

And they flee from such voices, from such words.

Stranger, Danger.

All scripture is given by inspiration of God, [2 Timothy 3:16, KJV]

Or, as Robert Young's Literal has it . . . . . 'is God-breathed' θεοπνευστος, Theopneustos.

The breath of God is in his word.

the words that I speak unto you, they are spirit, and they are life. [John 6:63, KJV]

Printed words on the page, alone, are lifeless.

And the vast amount of printed matter on earth is bewildering, if one has no Spirit within to lead one.

Sola Scriptura . . . . Scripture Alone, is where one hears a voice within, a Spirit's leading, another Life.

And, down through the centuries, sheep have collected the writings together.

Such as William Tyndale, who was betrayed, imprisoned, denied a candle in the dark hours that he might read his bible . . .. and was then executed.

But he left behind 'for every ploughboy in England (and the English-speaking world) - he left behind a collection of writings that sheep read, and sheep hear and sheep follow.

This is the way.

O thou fairest among women, go thy way forth by the footsteps of the flock [Song of Solomon 1:8, KJV]

Your main question is somewhat misleading. The debates over which scriptures should be included in the Bible canon predate the Protestant Reformation and ‘Sola Scriptura’. The onus on defending the canon falls on the men who agreed the canon at the Council of Trent in the 1500’s and not on the men who decided to exclude some scriptures that others claimed were divinely inspired.

The Council of Trent, held in the mid-1500s, considered such weighty matters as the Lutheran Protestant Reformation and how to counter it, disciplinary reforms in the church, the definition of dogma, and ways to establish key tenets of Roman Catholicism. It took 18 years, spanning the reigns of five popes, for the Council of Trent to actually convene. During the Council of Trent, both Scripture and tradition were declared authoritative for the Roman Catholic Church, with tradition just as authoritative as Scripture. Salvation by grace alone through faith alone, one of the Reformers’ rallying cries, was rejected in favour of sacramental grace and righteousness based on an admixture of grace and works.

The Catholic Bible contains a total of 73 books, 46 in the Old Testament (Protestant Bibles have 39) and 27 in the New Testament (the same as Protestant Bibles). The additional books in the Catholic Bible are known as the deuterocanonicals/Apocrypha. They are Tobit, Judith, 1 Maccabees, 2 Maccabees, Wisdom, Sirach (Ecclesiasticus), and Baruch. The Catholic Bible also includes additions to the books of Esther and Daniel.

By A.D. 250 there was nearly universal agreement on the canon of the Hebrew Scriptures, or what we call the Old Testament. The only issue that remained was the Apocrypha, with some debate and discussion continuing today. The vast majority of Hebrew scholars considered the Apocrypha to be good historical and religious documents, but not on the same level as the Hebrew Scriptures. I found an article that discusses the reasons why the Protestant Bible excluded the pseudepigrapha:

The first “canon” was the Muratorian Canon, which was compiled in AD 170. The Muratorian Canon included all of the New Testament books except Hebrews, James, 1 and 2 Peter, and 3 John. In AD 363, the Council of Laodicea stated that only the Old Testament (along with one book of the Apocrypha) and 26 books of the New Testament (everything but Revelation) were canonical and to be read in the churches. The Council of Hippo (AD 393) and the Council of Carthage (AD 397) also affirmed the same 27 books as authoritative. More information on the Muratorian Canon here: https://www.gotquestions.org/Muratorian-Canon.html

While the pseudepigrapha may be of interest to students of history and ancient religious thought, they are not inspired by God and therefore not part of the canon of Scripture. Reasons to reject the pseudepigrapha are 1) they were written under false names. Any pretense or falsehood in a book naturally negates its claim of truthfulness. 2) They contain anachronisms and historical errors. For example, in the Apocalypse of Baruch, the fall of Jerusalem occurs “in the 25th year of Jeconiah, king of Judah.” The problem is that Jeconiah was 18 years old when he began to reign, and he only reigned 3 months (2 Kings 24:8). There is no way to reconcile the “25th year” statement with the biblical account. 3) They contain outright heresy. In the pseudepigraphal Acts of John, for example, Jesus is presented as a spirit or phantasm who left no footprints when He walked, who could not be touched, and who did not really die on the cross.

There are many books that fall under the category of pseudepigrapha, including the Testament of Hezekiah, the Vision of Isaiah, the Books of Enoch, the Secrets of Enoch, the Book of Noah, the Apocalypse of Baruch (Baruch was Jeremiah’s scribe according to Jeremiah 36:4), the Rest of the Words of Baruch, the Psalter of Solomon, the Odes of Solomon, the Testaments of the Twelve Patriarchs, the Testament of Adam, the Testament of Abraham, the Testament of Job, the Apocalypse of Ezra, the Prayer of Joseph, Elijah the Prophet, Zechariah the Prophet, Zechariah: Father of John, the Itinerary of Paul, the Acts of Paul, the Apocalypse of Paul, the Itinerary of Peter, the Itinerary of Thomas, the Gospel According to Thomas, the History of James, the Apocalypse of Peter, and the Epistles of Barnabas. https://www.gotquestions.org/pseudepigrapha.html

To sum up:

• The Apocrypha was not formally/officially made a part of the Catholic Bible until the Council of Trent (mid 1500’s), in response to the Protestant Reformation.

• The early Protestant Reformers, in agreement with Judaism, determined that the Apocrypha did not belong in the Bible, and therefore removed the Apocrypha from Protestant Bibles.

• This begs the question, by whose authority did the Catholic Church see fit to include the deuterocanonicals/Apocrypha?