Many (too many) 'pure' SF writers have far too much of a bob on themselves! To them I say: "If you dislike what I say, Sir, you may send your friend to call upon my friend!"

As to tropes, that's been done to death. A trope is a convention specific to a particular medium, but not necessarily to a specific genre. LOTR is a novel about a covert operation to destroy or at least cripple the ability of an aggressor to make war, and the political process of creating a unified and peaceful world. What makes it Fantasy is the medieval setting and the use of magic. By altering the props, scenery and dialogue style, you could turn it into a war story, a Western ("Folks hereabouts call him Strider. Word is, he's one mean hombre!") a Space Opera or straight SF. If we must talk tropes, then the central one in this tale is a classic macguffin - the Ring - which could just as easily be a secret weapon, a vital piece of intel, a gadget or a treasure map.

Also, I dislike 'science fantasy' as a term. It's the kind of lazy thinking from 'authors' like Edgar Rice Burroughs who give their civilisations firearms to shoot down aircraft with, then invent a complicated system of 'honour' so thay default to swords for personal combat. Instead of sending it back to the author with a suggestion that they make/keep their technologies and cultures consistent and logical, equally lazy publishers just label it Science Fantasy.

Star Wars is Space Opera, like the Lensman series or WH40K.