Nuking any city in Europe regardless of occupation status with regards to the Soviets would have turned the entirety of Europe against the U.S. in a heartbeat. At most, they could have nuked Eastern Russia, which, while not good, would not help them in a theoretical Western theatre.

You are vastly overestimating the capabilities of nuclear weapons of that time period in a conventional war and vastly underestimating the political costs of using them. The only reason we got away with using them on Japan is that, we won the war, we rebuilt their infrastructure, and because everyone was incredibly racist with the exception of the Soviets who were only a little racist.