Bernd,
What a shame. Guess a multi user system is a lot to ask for.
Just please please please do NOT take the easy safe route and ban PM+ from storing catalogues on a server share (that's what Adobe did).
We won't likely ban anything, but it will corrupt the DB if you open it simultaneously from two different computers.
Any chance that we can get the other functionality I asked about (directory structure for Windows 10 and Mac OS identical/exchangeable)?
Is there a common mount point (a folder) where the macOS system and the Windows system provide the directory structure in your topology? For instance, do you have something like this?
Server Name
Photos
On macOS, path is: /Volumes/Server Name/Photos
On Windows, path is Q:\Photos
If you're going to have only items at the folder "Photos" or below then we would likely be able to solve that.
-Kirk