When are you not allowed to park on the right-hand lane?

You answered correctly. In German traffic rules, you are not allowed to park on the right-hand lane if there is a properly paved hard shoulder (because parking should be on the hard shoulder), if rails are installed in the road lane (to avoid blocking trams or trains), or if there is a designated parking lane to the right (because you should use the parking lane). This ensures that the main road lane remains clear for moving traffic and special vehicles like trams. Always look for alternative parking areas before stopping on the main lane.