Aeroflot can accept US credit cards directly but the devil is in the details of how the credit card is processed and the sell-side's risk tolerance for payment disruption.

By the way, Americans attending concerts in Helsinki (Finland) and paying by cash or card this summer for shows in Helsinki may be violating US law if this sanctions situation is not ratcheted down well before then. Non-Americans abroad can enjoy those shows and buy tickets to their hearts' content compared to Americans. Welcome to the world of economic sanctions in play.