Specifically, in the Ukraine, these extremists want Ukraine to be a White ethno-state. They subscribe to the Great Replacement theory, which came out of France about a dozen years ago. It’s anti-Semitic and anti-Muslim, mostly. They believe Whites are being systematically replaced, by design, via mass migrations. All orchestrated by the Jews. The black sun is a Nordic symbol, but it has been coopted by groups who subscribe to this theory.
If being against mass immigration by Muslims makes one a “white supremacist”, then many (most) on FR are in that category.