Trump

[Keef]

Tbh I have no idea how folks who went to fight Russia got there or came back.

American to Turkey flight, Turkey to Armenia/georgia/azerbaijan, from there to Moscow, rock up at a recruiting office is my best guess.
Having googled it USA to Turkey, Istanbul to Moscow.
Coming back would be trickier because of the Russian visa and stamp in the passport, and maybe try lying by saying it was for work closing down the Russian business operation due to the sanctions