Spell checking just doesn't work... as far as I could tell, in all of the apps for Lemmy (at least the 3 or 4 others that I tried apart from Jerboa) and I have no idea why this is.
I have Gboard set up to underline and suggest corrections, not actually auto-correct, because English is not my native language and I use Latin the Latin keybord (mostly) for my native language as well, so it doesn't auto-correct the words when I communicate locally.
Tried SwiftKey, but it doesn't have any options regarding spellchecking, it just has auto correct, suggestions and that's it... so it doesn't actually suite my needs.