Completely reset all keyboard related configurations? (Media keys and mouse click with macro keys not working)

I recently asked this question, but both didn't get a reply and have more information. My goal is to get my keyboard (Sound Blaster Vanguard K08) fully working again. Currently, the macro keys only work if I put keyboard buttons/combinations on them, but not mouse buttons, and all media keys are dead.

However, when booting from the Ubuntu 19.10 Live USB stick, with which I installed my system, everything works perfectly fine.

How can I get back to that state? Any suggestions are welcome.

My hunch is, that my keyboard used to be recognised as keyboard+mouse or sth like that, because special and mouse related functions don't work anymore.