Thank you, Umberto.
It was a while ago when I configured GSX in MSFS 2020 to enable seated pax, and I remember I had to tick some boxes (if I remember correctly) in the config screen. For some reason, however, there are no aircraft showing up in the config screen, even though I have the 777-200ER and -300ER from PMDG installed. As far as I can remember, supported aircraft should show up in the config screen, under the Seated Passengers window.
Chances are that I am missing a step. Can you please help me out?