Cannot type letters with a numeric keyboard (T9 keyboard apps won't launch)

[tea-enjoyed]

Hi, I have a phone with a hardware keyboard on it, and I use Traditional T9 (It's on github) to write text.

Unfortunately, when I launch a session, I cannot use Traditional T9, or any other keyboard client (I tried simple keyboard (from F-Droid) and Kika (Another 12-key client) , both failed) besides GBoard, which functions as expected. This is quite a bummer because the screen is very small and I would have loved to be able to use my T9 keyboard to execute commands.
From what I know, this hasn't been fixed yet. (Because pretty much everyone with a normal smartphone uses GBoard)

Is there a way for me to fix this by myself? If not, could the contributors do something about this?
Thanks in advance.

[tea-enjoyed]

Edit: My bad, I just checked the issues and found someone with the same problem as me. However, I'm still open to an answer.