Swastika is common to many ancient cultures predating Slavs and their ancestors PIE dated to 8-10K years before present. In different cultures swastika meant different things. It is excepted that swastika is a solar symbol in Slavic cultures. I don’t know if Slavs adopted the symbol looking at Ursa Major (Large Chariot is people’s name for tje constellation in Belarus. Probably in Ukraine too.) I am guessing Slavic ancestors took the the symbol from their ancestors, who in turn took it from their ancestors and so on.