As explained so many times on the forum, in order to see passengers, ALL the following must be true:
- The airport must have SODE jetways. It doesn't matter if it's supplied with the scenery, or replaced by GSX. But it must be SODE
- The jetway must have docked
If any of these conditions is not satisfied, the passenger boarding will be simulated. Of course, GSX Level 2 must be active as well.