When creating a new connection in a Mosaic model, the mandatory “Database Version” field is empty and the dropdown does not display any options to select.
For instance:

One common cause of this issue is that the user lacks access to the DBMS object.
Review the security settings on the DBMS object and adjust them as needed for the relevant user or user group.
Workstation > Data Sources > Gateways > Change the security access on the required gateway.