There may be a few white supremacists mixed up in the protests, but I don't understand how they could be organized to the point where they're burning and looting buildings. White supremacists aren't very smart, and they're definitely not organized enough to pull something like this off. Further, white supremacists are celebrating Floyd's death, I don't see why they would have any interest in traveling to a city in which black people are protesting the death of a black man via a white police officer. Again there may be, and probably is a few of them there but it's not organized. If there were actual organized groups of white supremacists there I can't envision how they would not be fighting black people.
I'm not saying this to defend them, it just doesn't make sense to me. If I had to bet, the white people primarily involved in the looting and burning are 18-30 year old Bernie Bros. There is a crazy faction of Bernie Bros and unlike white supremacists, this is an issue that would actually piss them off and draw genuine anger.