Look in Reliability History/Monitor and Event Viewer for any error codes, warnings, or even informational entries being captured just before or at the time of the shutdowns.
After the next sucessful boot run "dism" and "sfc /scannow".
This worked, thx !
Here the report:
C:\Windows\system32>sfc /scannow
Beginning system scan. This process will take some time.
Beginning verification phase of system scan.
Verification 100% complete.
Windows Resource Protection found corrupt files and successfully repaired them.
For online repairs, details are included in the CBS log file located at
windir\Logs\CBS\CBS.log. For example C:\Windows\Logs\CBS\CBS.log. For offline
repairs, details are included in the log file provided by the /OFFLOGFILE flag.
P.s.
A year or so ago, I was too lazy to reinstall Windows and all my programs (mainly the programs), so I cloned my Windows installation from one SSD to a faster SSD. Except for one program, everything worked fine.
Maybe that caused some issues, or perhaps it's a hardware error. I know my PC is a bit old, but I only upgrade when I have to.