SQL - "Error with query"; it was not possible to establish a network connection to the server

We installed a fresh copy of SQL 2019 on a windows 11 machine.

The old sql server can still be accessed flawlessly from BE.

The new one ist visible after installing the agent; also SQL Server is listed as an separate item and also the instance is visible (MSSQLSERVER).

Buut, we cannot see the DBs

the detailed message says something "QeureMetaData: MDQ_ ....." later I see the FQDN of the SQL Server, but not a detailed error message or the reason for the failure

the server can be accessed from SSMS and also from the BE Server via the ODBC configuration app. (using the system login account)

What can I do to drill down the problem?

P.S.: I can see all dirctories on C:

Otherwise Systemstatus takes a couple of seonds to list, but finally it works