I tried Thumb-Key. Learning curve was really high. I instead went with Unexpected Keyboard, also no predictive text. I really enjoy using Unexpected Keyboard and I don't have to through a bunch of sub keyboards to look for a symbol. I rarely go to a different sub keyboard.
Do you type faster with Thumb-Key than a normal keyboard like GBoard? In your opinion, is it worth learning?
Thank you for your input. I think I'm gonna give another try.
Note for other readers, Traditional T9 is a keyboard available on F-Droid.