I was in the same boat until a year ago or so. FUTO^[1] finally provided a good text prediction/correction pair + that simply better feeling the Gboard has^[2].
[2]: I never investigated this, so I always assumed that GBoard predicted what key I wanted to press when close to two letters. With FOSS keyboards, with a physically identical layout, I tended to make way more mistakes.
I find GBoard to remain superior in multilingual typing, futo just can't seem to be able to switch to other languages consistently, even with the multilingual option enabled,
it's also not as good at "recovering" from typing too many letters (Gboard sometimes adequately completes with likely shorter words)
I don't think I ever tried this one. I think I tried every keyboard on F-Droid but apparently FUTO isn't in the main F-Droid repo. I'm liking it so far. I'm a swipe typer and on most keyboards the swipe functionality is much worse than GBoard but this one seems to work pretty well. I'm going to try it for a while, thanks for the suggestion!
Gboard is somehow still the best, the native android keyboard is hardly usable. I use it on GrapheneOS, but with network permissions removed. Haven't had an issue so far
Evidently some disagree, but I'm on your side. Biggest reason I didn't immediately think of "But what would I use for a keyboard" is my Q25 has on built-in.
UnifiedPush, F-Droid, a GMaps webview (arguably cheating, but I'm not RMS), NewPipe or Invidious are all good-enough alternatives, but I remember struggling to find a keyboard that felt right when I was using a Pixel 2 for a fortnight.
I think I went with the oldest Fleksy or Minuum APK I could find (from a reputable source), as they were fine without GApps.
Though I'd also like to call out the fact that AOSP has talkback, the accessibility service built-in, but there's no AOSP TTS engine to use it with. This is especially noticable when trying to use any spoken directions in OSMAnd, as it requires a TTS engine to use that function.
The only reason it's not the dumbest thing about Google's stewardship of AOSP is that I'm not sight impaired - as it stands, the multi-trillion-dollar corporation ripping out the built-in SIP client in their phone OS takes that prize
[1]: https://keyboard.futo.org/
[2]: I never investigated this, so I always assumed that GBoard predicted what key I wanted to press when close to two letters. With FOSS keyboards, with a physically identical layout, I tended to make way more mistakes.