That brings back pre-iPhone memories!
I’d start by seeing what the Keyboard object returns when a key is pressed (just numbers I’d guess). Then see what happens when you type into a Text Input object.
Did bit of experimenting. When activate text input it immediately calls for keyboard app like Gboard or Old T9 Keyboard. Trying get inputs from keyboard plugin no results. Looks like it has some proprietary system. But then Old T9 keyboard app reads inputs of device and corresponds to a key so there is either using some more deeper stuff that Construct 3 can't access or it's just engine throwing fit because well it's odd device
Edit 1 (there gonna be a lot)
While starting test inputs weren't recognized but after switching into text input then switching it off I started getting input codes off keyboard raging from 37-40 for Navi and 48-57 for numeric so some sorta keyboard emulation is but it's not immediate gonna build APK and see maybe it's issue with focus
Edit 2 (perhaps final)
After building APK and testing on phone got immediately reads of input keys showing issue was with focus. In theory it's possible to write native game for this specific device since keycodes will be different for other similar devices like Cat S22 but it looks like on some free time when not be on main project will write small game using it's physical input or mix both touch-screen and T9 keyboard