Per your link, 80% of black men supported Biden. Given that mail in ballots have tended to be in Biden's favor, in large part because Trump asked his supporters

Per your link, 80% of black men supported Biden. Given that mail in ballots have tended to be in Biden's favor, in large part because Trump asked his supporters to vote in person, I don't think it's a stretch to see almost all mail in ballots from black areas going to Biden.