I tested OSMC:
1. Connected the NFS device at the RPI bookworm but not with the QNAP, so was unknown to the system
2. opened the playlist file
3. run a youtube link
same error -> has therefore nothing to do with the missing NFS connection to the QNAP, or?
-> originated in Kodi itself, or youtube addon?
I looked in the error log and it said frequent "NFS Mount error" but why? The link I opened was a YT link.
The explanation I have is that Kodi, despite I want to open a YT link, looks inside the whole playlist file for invalid links. So, I made a playlist file with only YT links which are valid and voila, error gone.
Kodi looks into all playlist file links if they are valid (?)
After this error, Kodi is slow. In older versions of Kodi, it was different.
OT: In OSMC the youtube addon has problems by itself