After hours of research, I had found people who had stability problems with the r8169 version of the various realtek in the kernel so I had resolved to stay in DHCP (because the problem was solved).
Aus der Community linux4noobs auf Reddit
Entdecke diesen Beitrag und mehr aus der Community linux4noobs
www.reddit.com
But last week I saw a firmware-realtek update in OMV
firmware-realtek:amd64 (20241210-1~bpo12+1, 20250410-2~bpo12+1)
And having switched back to IP static to test, it seems that the problem has been solved with this update.
I hope there won't be any more problems