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.
It's a prediction market and you can bet 'on' Trump or 'against' Trump. Betting 'against' currently pays 1.072 and there's .1 BTC you can take at 1.069 odds. These are pretty good odds that are significantly higher than predict it, but I guess a lot of people are confused as to how prediction markets work.