Creating/printing labels from odb-Database

I am on LO 7.2.3 and Kubuntu 20.10 (also got 7.0.x on my system, which acts the same unsatisfactory way).
I am trying to create labels from data in a MariaDB database table. However there is one big problem: My database is not recognized when specifying dbname, table and table fields. However, I can definitely display the db and table quite normally otherwise, create new tuples, move data to a spreadsheet, etc.
I am “sunk”. Can anybody help?
H. Stoellinger

EDIT @Hrbrgr | Thank you for using the English page.

Open some Writer document and call menu:View>Data sources… [Ctrl+Shift+F4]
Do you see your database with tables and queries stored in the odb document?
If not menu:Tools>Options>LO Base>Databases and add your odb document to the list of registered databases which are accessible for all documents.