I still don't know how Tucker was allowed to travel to Russia, I thought that there was a travel ban at the time

There's no US ban on American travel to Russia, and I dont think there's ever been There's been the highest warning of course due to potential harassment and arrest and the limited consular help State Dept could offer. Think N. Korea is the only country with close to a full ban, Cuba w/ exceptions

There’s been a ban on US persons visiting Cuba without a license for decades; AFAIK it’s not infrequently violated and prosecution is rare. (As someone who has visited Cuba with a license, tourists are better served by a large number of Caribbean destinations.)