The Hiroshima shadows.

[Gawdzilla Sama]

Berlin wasn't nuked because the Germans surrendered 2 months before the Bomb was ready.

Even if the US had the bomb in time.   Berlin was allocated to the Soviet Union. It was evident Stalin would pay any price to take the city.    It was clear the soviets were going to take most of the remaining allied casualties needed to subdue Germany.   In the end the soviets suffered half million casualties in taking Berlin.  The US was not about to nuke the city and risk weakening German defenses and allowing the soviets to take the city more cheaply.

In any case, Berlin was still one of the world's Great metropolis, on par with London, Paris or Tokyo and much more important than Hiroshima and Nagasaki.  It was clear German ability to resist was coming to an end.  Nuking Berlin could have very damaging effects on European public opinion, and hand the soviets a great post war propaganda gift.

There was no analogous condition with Hiroshima and Nagasaki.  It was widely believed the Japanese still had plenty of capacity to resist, the two cities are relatively minor urban locations.  If the war were to continue the US would absorb the bulk of remaining casualties required to subdue Japan.

Eisenhower made the decision to stop short of Berlin. That had nothing to do with the strategic bombing program. And Hiroshima and Nagasaki were prefect capitals, and the military command centers for their areas.