Thank you.
This is a reply to both Steve and Phillips.
It seems there's a great misunderstanding on my part. The quotations you present are explaining why, in certain situations, charging stops at 80%. This is clear and does not require Apple's algorithm to explain it. My situation is the OPPOSITE. It used to be 80% for 15 months and then suddenly stepped up to 100%, while there was no change in my usage routine.
Moreover I have a very strong feeling the change took place immediately after upgrading to OS 12.3.1.
It is very difficult to believe that suddenly 100% charge becomes the optimal. I wonder if any other users have noted this change. Perhaps something is wrong with my machine, I do not know.
That said, I doubt we can solve the problem here. I think best action for me is to unplug from power adaptor from time to time, work down to 20% and replug again, while waiting for a new OS update that might resolve the optimal charging issue.
I had similar situations with this computer (M1 - Big Sur - Monterey), such as 25-30 minutes to launch Mail on Mac, complete shutdown after putting computer to sleep, and more. Those were eventually fixed by the guys at Cupertino or Herzliya. (The latter is situated 1 km from my home. I pass there every morning on my daily walk, but they won't let me in to talk to them....).
Thank you so much for your help and time. I'll keep you abreast of developments.