disassemble it and wash the plastic with a detergent or sth

The coating is insanely hard to get off like it is, I think It is simply too much effort for a 20€ mouse.
I think I would need to let it soak in strong stuff like rubber alcohol, then scrape it off without getting too much contact in the process (because cancer).
I tried heat and strong cleaning detergent, does not work. Maybe sunlight might dry it out?

I wonder what kind of reaction even caused this, there was no plastic in contact with the mouse.

heat and time probably caused it. You could try sanding it maybe

try heating it up again with a fan then try to wipe the coating with some idk gas or paint thinner. or try to rub it down with sand paper.

OR you can just respray some clear coat over the surrent rubber and see what happens... whats the worst then can heppen? ... shrooms start groving form mice? ... its a win win if you ask me. :)

the best way to clean it was using wet tissue, wet wipe, baby wipes.

i have read it and tried it before with good result.

The same thing happened with my Razer Copperhead. Left/Right buttons are sticky. I just put some water on a towel and just scraped it off. It's still a bit sticky I'm going to try putting some googone on it.