UPDATE: I was able to find a previous firmware version (2.2.2 / December 2019) using webarchive:
http://web.archive.org/web/202006091...s/#note-series
I downloaded it, copied it over USB in my Note root directory, installed it using the Firmware Update section in Settings. The downgrade succeeded, this firmware version is much faster than the latest one, but the stylus still doesn't work, so I guess the next step would be to try another compatible stylus, then to disassemble the Note and check the screen model and connectors, maybe I can find a compatible one to buy at an affordable price. Will a N96 fit?