White Supremacy somehow became intersectional in 2020.

The real answer is that Whiteness has always been an extremely flexible social construct that is used to weaponize violence against an out group. Who is and isn't White has changed dramatically over the last four hundred years, with groups being included as "White" based on the needs of the ruling powers at any given moment. "White" varies wildly from place to place and culture to culture. There are "White" people in Jamaica who would be black in America, "White" people in India who would be considered Indian in America. Famously Italians became "White" in the 60s, Catholics were only grudginly White before that.

The Proud Boys can have some token mixed-race and dark skinned people included in "White" because it's convenient and gives them the numbers they need to enforce racial, gender, and economic violence.

It's worth remembering that even the Nazis felt that the US's "One Drop" rule, where "One Drop" of African blood made someone legally black, was too harsh.