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.

I know nukes are terrifying and cause lasting environmental damage, but back then and even now, conventional warfare still dominates if you want to control territory. Nuclear weapons are a little overrated in their full effects honestly.

Nukes are good at horrifying surprise attacks. They're terrorism weapons. If your goal is winning a war and holding territory, you're still going to use artillery, airplanes, troops, and drones.

The scary part of nukes is when your opponent also has nukes, so is also able to do sudden nightmare attacks you can't expect or defend against. Nukes also make everyone on earth hate you. They have a political cost of making you seem untrustworthy or insane.