How to play DVDs (and possibly BluRay)?

Tried to play a DVD on my Vero 4k today, but to no avail.
OK, checked installed packages and install libdvd-pkg (and libdvdcss subsequently) as well as libdvdnav4 and its dependencies. Nevertheless - the DVD won’t even display a single second, a menu or anything. (AVATAR)
Other DVDs are playing fine, e.g. SKYFALL

How can I figure out what is the cause of this?

This could be a problem with the copy protection of this dvd.

It would be good to see some debug logs to identify the problem.

See here:
https://osmc.tv/wiki/general/how-to-submit-a-useful-support-request/