I can't speak for the other wars he's trying to withdraw from, but the outgoing Syrian envoy lied about the number of troops remaining in Syria. Initially Trump wanted to withdraw entirely, but they recommended keeping 200 soldiers there to avoid that power vacuum you're talking about. Then they proceeded to lie about it.

Which will be very convenient for the upcoming conflict in Syria once Biden gets into office!

https://www.defenseone.com/threats/2020/11/outgoing-syria-en...