Yes, you can bet on whether Joe Biden will drop out of the US Presidential election race...if you're outside of the United States. The most prominent place where you can bet on this (in either direction) is Polymarket. Polymarket is a prediction market that allows you to buy contracts on 'yes' or 'no' for a wide variety of events. However, Polymarket isn't available to customers in the United States, and is unlikely to be anytime soon.