as I can see, this question was answered by our servicedesk.
I will copy the response here in case someone else faces the issue:
“DataStore: Unavailable” means that the data for this table is cached data. As the customer described correctly, this happens when the table was imported via transport; the transport doesn’t know anything about the original DB connection, it just contains the data itself as files.
To set a DB connection for such a table, you can use
table.set_db_connection(<DBConnection>, <table name in the database>)
Then it should change the data store of the table accordingly.
So you just need a DBConnection object which should be set. If there are already connections defined in the datamodel, you can get all DBConnections for a DataModel with:
connections = datamodel.connections
Alternatively, if no DBConnection is contained in the datamodel, a new one can be created with DBConnection.create_new(…) or you can create it via the frontend first.