Hi Alexandre and thank you for your reply.
I’m sorry for the inconvenience, but I solved the problem on my own. I found out, that I was using an older version of the document server (5.5.0.165) from a different repository and after upgrading to the official docker container (from Siwat2545’s Repository), I can upgrade to OO 7.2.0 in Nextcloud without any issues.
The unraid version is 6.9.2, NC version is 22.2.0, OO document server version is 6.4.
Maginos