Are there any bitcoin sites still taking wagers on this?
Fairlay.com are still accepting US presidential election-related bets (buying and selling on both sides).
From fairlay, I only see the option to bet on Trump, not Biden.
https://fairlay.com/markets/news/This is a joke, probably it's a sucker bet because Trump had no chance of changing the votes, therefore he will loss pending the formal announcement of the election, I doubt there are still bettors would would take Trump despite the news all over that Biden is 99% likely to win the election.