File sharing with OpenDirectory network users

I am upgrading from Mac Mini macOS Mountain Lion Server to MacPro macOS Catalina Server.

I learned that most of the needed server components are not anymore available.

But file sharing and user management aka OpenDirectory is still available. According to this guide by Apple it should be pretty straightforward:

1. I enable file sharing (SMB, because of APFS) as part of the preferences.
2. I add the folder to be shared.
3. I add the allowed user accounts next to the shared folder. The user account can be a network account (or group).

But that does not work. Only the local user account can access the shared folder from another Mac. The network account is always denied.

The network account is entered in the Server Tool. Open Directory is also enabled as the Master. In the Directory Utility I can see that the network account is available. What I can see is, that the network account has no Kerberos Credentials setup, but the local user account has those.

Is there something I need to make sure to enable network accounts from the Server admin?

I don't see what I have done wrong. There is not much left to do something wrong, as there is not much left in the server tool at all.

MacOS Server used to be a pretty good tool, especially on the old Xserve with LOM. But his actual thing seems to be a wrong move.

Thanks for some hints and advice.

Thilo