In my F-Droid, there's plenty of other! Eternity, Liftoff, Jerboa, Thunder, Voyager, Lemmur and Combustible when I search for "Lemmy". Maybe you don't have all/the same repositories enabled? I'm using Liftoff at the moment, which is great so far, but I haven't settled yet. I want to try using some of the other ones before I'm sure. For reddit I used Joey, and I would consider switching to Joey for Lemmy if it existed.