UPDATE
This morning I bought a new mouse, but it sucked so much that I ended up opening again the old one to see if there was really nothing that could be done.
TURNS OUT THERE WAS
the component themselves were working, as evidenced by the fact that, once I opened the mouse, I could use the switches to click. The problem was that, since the left button is subjected to a lot of stress when I paint, draw or play, the trasmission part connected to the plastic body had worn out so much that it was pulverized in places and it was no longer reaching the switch. I put some duct tape on it and now it makes contact again :D

WHEEEEEEEEEE
ALSO TONIGHT I MET DAEVION: YESTERDAY WAS A BAD DAY, BUT NOW I’M HAPPY