If I'm correct in my assumption, I think I know why he's looking for a black female running mate:
1) They're mad they didn't get their precious "woman" president after their "black" president.
2) They're making sure it's a black woman so (a) people don't get mad about "white woman privilege" and/or (b) making sure they actually have a first black president when Biden keels over or derps himself out of office.
The solution is simple: if Dems really want to win, they should have Bernie Sanders be his mate, and Sanders could just identify as a black woman. Tolerance, amirite?