Was swastika really a popular symbol among Slavs and/or ancient Indo-Europeans?

To elaborate a bit on climenole's answer I'll add a bit of math behind the swastika symbol.

Swastika in both clockwise and counterclockwise direction has been, and still is used in many cultures. In some areas of modern India it remains to this day as one of the symbols used to decorate the bride during wedding. The logic behind that symbol is actually straightforward: swastika is rotationally symmetric but not mirror symmetric. It kind of rolls in one direction, if you take the legs as directions, but not the other direction.

Consider, for example, a square. You can rotate it as well, but there is nothing to indicate a preferred direction of rotation. Mathematicians would say that a square has symmetry group $D_8$, which includes both 90-degree rotations, as well as mirror symmetry, which postulates that it's impossible to make any convention for the preferred rotation direction. Swastika, on the other hand, has symmetry group $Z_4$, which allows to establish a convention for the preferred direction (such as "where the legs point to", for example)

Since ancient times peoples half the World apart have noticed this asymmetrically symmetric feature of 3- and 4-leg swastikas and used those symbols to indicate unidirectional movements, such as "going only forward, never backward". Therefore the symbol could appear quite independently in various cultures.

I'm not sure the confusion here as the symbol is well attested in ancient Europe. The earliest finds of the symbol come from Eastern Europe.

The earliest known swastika comes from a figurine carved from mammoth dated to around 10-12,000 years old. It comes from Mezine in Ukraine. The word swastika is from sanskrit, from India, but the symbol itself is first seen in Eastern Europe.

A swastika was found on pottery from Riben, Bulgaria dating 7000 years ago, this is around when the Indus Valley civilisation began. The mammoth bone swastika mentioned above was already 5-7,000 years old at this point.

Obviously too, this was several thousand years before Indo-Europeans (IE) moved into Europe. I'm unsure of the relationship between the IE and the earlier people of Eastern Europe but the IE certainly use the swastika later themselves in much of their art. It's a common motif in Greek, Etruscan (non-IE) and Roman art. The Celts used it, the Germans used it, it's still a popular symbol in the Baltic states and is used in IE and non-IE states alike.

It's use in Europe dropped off after Christianity became widespread. It saw renewed interest in the late 19th century with the rise of interest in archaeology and the distant past. This culminated in a burst of popularity of the symbol where it appeared on everything from bottle openers to sports teams. This popularity was stopped short once it became associated in the press with the nazis during the 1930s, who had adopted the symbol themselves for its links to Germanic paganism - though they adopted it via the Thule Society who funded the nazis early on.

Here's something for a bit more information and an interpretation of how the swastika came into being:

https://www.academia.edu/11165695/Swastika_was_used_in_Neolithic_Bronze_and_Iron_Age_cultures_and_its_probable_origin_is_from_Astrology

The swastika symbol was used by many cultures in the history and around the world and not only among Indo-Europeans.

For example swastika is used in Far East (China, Korea) as well as the Wyandots (Wendats or Hurons) in North-America. You can find this symbol in ancient Greek potteries as well as decoration in Christian churches too…

This was often viewed as a solar symbol but also, associated with a rhombus. The swastika as male symbol and the rhombus as female symbol.