Alternatives to Gboard

Works on MicroG?

Works, without sync

Open Source Offline

AOSP Keyboard

Simple and almost always reliable. Already included in many custom roms

OpenBoard

It's like AOSP but with more functions

AnySoftKeyboard

Any Soft Keyboard is an open-source, on-screen keyboard with multiple languages support with an emphasis on privacy.
This is one of the most customizable keyboards available.

Closed Source Sync

⚠ Privacy Alert: All closed source keyboards indicated send some personal data to their servers. Please read the Privacy Policy of each service. Try to block internet access if you want to use theme offline.

SwiftKey

No description required

Typewise

Seems to be privacy friendly, try it

Touchpal Lite

It has lots of functions, and it's very reliable