Inserting rows in Mendix tables yourself (using Java or other form of SQL insertion) is not supported nor recommended. You should use the "Create Object" activity in a nanoflow/microflow, or use the Mendix client/Java API to create an object of a specific entity to insert a row in a table.
See also:
https://community.mendix.com/link/space/databases/questions/105250
https://community.mendix.com/link/space/java-actions/questions/119174
This old thread might give some more insight into how Mendix generates the identifiers, but again I would never do this:
https://community.mendix.com/link/space/app-development/questions/4441