I'm not questionning, just sharing a positive experience, for those who encounter similar problems.

These last days I was going crazy with the Finder freezing randomly, but also other apps, forcing me to hard reboot each time. Running Big Sur on a Mini M1. I called Apple for help, and I had a long conversation with a nice lady. She said I should upgrade to Ventura, that the engineers would require it anyway before looking at my problem. So I updated all my back-ups, and went on installing Monterey 12.6.3 on an external drive. As it looked OK, I decided to try it on my main disk. Upgrading from Big Sur 11.7.4 to Monterey 12.6.3 took about an hour. Well, so far so good. All seems to be working smoothly and no problems at all after a day. Also, my favorite apps and personal settings, shortcuts etc.. are working fine. I'll come back here if the bad issues return.