Sorry to all of those who had this happen to their Macs. I wonder if restoring through recovery (Cmd R booting up) would solve the issue?
I have a Mac Mini late 2014 with 4GB Ram and running at 1.4GHz with a non Apple SSD (installed by an approved Mac Apple Store: I brought in the SSD I bought in Amazon).
This Mac bought as second hand on the Mac Store has worked like a charm from the moment the SSD get installed, that is in 2018, before it couldn't beat a snail. This was with Mojave.
The update for Catalina worked also great but there was problem in double screen scenario.
Whatever I religiously not upgraded to Big Sur: got an intuition that would not do the Mac any good.
And I wait to upgrade to Monterey till march 2022. The upgrade worked perfectly well.
BUT 15 days later, the main uset account started to turn very very slow, in fact freezing. No freeze, no lag on other users.
After troubleshooting, I couldn't find out the root cause: I disabled Spotlight, cleared all caches, repaired the disk permissions -> NO changes. It was very very odd. Found out it was probably caused by windowserver. I did PRAM and SMC reset, no change.
But why no problem with other users?
I decided to completely reinstall the OS, wiping out the drive and using a time machine backup from start of March 2022. And there after hours of copying, the Mac got the switch off automatically after 15 secs boot.
I said to me, "OK, let's do the wipe out of the SSD and install OS from internet", 5 hours download and install, same kill switch boot. But the hardware works: it's able to download for 5 hours, able to install.
Strangely I tried that several time and each time it was a different OS version which was installed: high sierra, mojave, never big sur nor monterey. This look like Apple is behaving the Microsoft way where computers are completely out of control and undecipherable beast.
SO? I strongly smell politics and Apple pushing people to upgrade to new hardware. But more than that I feel the end of the US empire: the States are in fire, nothing runs good anymore there and from there, it's complete chaos.
Now the Mac mini is bricked: I searched for a firmware upgrade but this Mac has none AFAIK, it has no T2 chip so no DFU AFAIK, and 2 days lost... maybe I can turn this dead horse into a linux machine?