So, now there's no need for MATVT or C9 or messing with Shizuku anymore, because it turns out Sonim dumbphones already include a native system mouse implementation, but there was just no way to enable it normally! So, it's usually only visible in their Browser app.

This small app lets you toggle the system mouse with a programmable key, so you dont have to rely on third party mouse implementations whose functionality can vary.