Suddenly the MSFS do not start, just a small error message is shown (repaired)

Today I’d like to start the MSFS but it won’t. Immediatly when the icon is clicked (to start) then a small pop-up window appears:

"Es liegt ein Problem mit Microsoft Flight Simulator vor. Führen Sie eine Neuinstallation der Anwendung vom ursprünglichen Installationsverzeichnis aus, oder wenden Sie sich an Ihren Adinistrator."

Some days ago it was running fine. On the PC nothing was changed/installed/deinstalled. Very strange.

Detailed steps to reproduce the issue encountered:

nothing, just double-click on the icon to start MSFS

PC specs and/or peripheral set up if relevant:

intel I9 10900, Nvidia rtx 3080, 32GB ram

Build Version # when you first started experiencing this issue:

SU8

Wassat in English?

no, german. My Windows is set to german (i’m nativ german speaker)
on my pc almost all apps are running in german

To translate the error message:

This app con not be opened. The MSFS encounters a problem. Install the MSFS new from the original install folder, or ask you administrator

link to picture, pop-up message

The problem was not found, however it could be solved. But it is unknown to me, what really happend.
The windows event log showed a lot of errors, e.g. certificate errors, OSR server failures and other messages, which I do not understand. OSR server might relate to the Oculus software.

It was luck, that a Windows restore point (4 weeks old) was available. The PC was restored and until now it runs. The MSFS runs, too.

So, the problem was a PC problem, not the MSFS.
Now I have a bad feeling about win11.