I’d like to play some ScummVM games that fit perfectly on the GameShell, but it works only with a mouse to control the cursor, there’s no way to bind some keys to do that on ScummVM.
I know nothing about Arduino or keyboard drivers.
Alternatively I found this, which maybe could work, but it’s a different thing, it’s rebinding the keys through Python. I’ll try to do this at once, but was still wondering, could be interesting 
This seemed too convoluted so I tried once more running ScummVM inside RetroArch and managed to do it by compiling ScummVM directly on the GameShell. A link to the compiled file and instructions on how to do it is on this post: https://forum.clockworkpi.com/t/running-scummvm-games-on-retroarch/.
Should I delete this post?
Yes it can: https://www.arduino.cc/reference/en/language/functions/usb/mouse/
Although you would have to modify the https://github.com/clockworkpi/Keypad/blob/master/clockworkpi_keypad.ino