That is why I used the word speculation, because in my reading about FDR and Churchill I have yet to find anxious discussions about the German atomic bomb.
If I remember correctly, they stopped working on it because they were too focused on their other super weapons.
One of the things about a German bomb is they would have had to live with the fallout—even if they won.
On the other hand, the US could drop them with impunity because Japan was an island and the radiation wouldn’t hurt anyone else.