Florisboard is great and opensource

Even without any permissions, GBoard has additional services on which link to Google Play services. You can check this by going to developer options under system setting and clicking on running services.

I like Futo and Heliboard, Floris is also good. For the average person coming over from stock Android, GBoard remains the best feeling keyboard tho. The open source keyboards just can't quite match the haptic feel and autocorrect abilities in my experience. They're all fine tho if you're willing to take a bit of a UX hit for improved privacy.

FUTO keyboard has the features I missed from Gboard.

I find the autocorrection to not be as good and it's a huge annoyance when I have to go retype every 3rd word. Just my opinion tho. I do like it has glide typing tho, that's essential for me. This message was typed with FUTO