maybe for other worlds, but the kayfabe of Tolkien's works is that they are historical accounts from our own real world. canonically, thousands of years after the end of the Third Age, Eru Ilúvatar sent himself to Middle-earth in the form of a Man who was his son, and he was called Jesus Christ; at one time Tolkien said that was the beginning of the Seventh Age, which we are currently in

essentially that means that whatever happens in the real world, or at least wherever happened between events recounted in the Bible up to 1954, is canonical to LotR. so we have explicit confirmation that it would have been physically possible, given the proper technology, to drop a nuke on Sauron

but the things is that it still wouldn't have happened. because recognizing the danger of great power and seeking to use it to your own advantage to dominate your enemies, rather than acknowledge that it should not be used by anyone, is what the dang book is about. the whole point is "don't do that exact thing." anyone in Middle-earth who would use an atomic bomb either is Sauron, or serves Sauron, or would at best defeat Sauron in order to take his place