Thank you Paul and John for the quick answer!
According to this document https://dokumen.tips/documents/pmdg-737ngx-custom-event-ids-for-use-with-fsuipc-and-fsx-fsx-se-or-prepar3d.html , these three button do have cutom evenIDs associated to them, these are 69810,69811 and 69812. When going through PMDG_777X_SDK.h, there is no var for the buttons in the PMDG_777X_Data structure, but events exit.
Now when used the FSUIPC logging as you suggested, I couldn't see such events. As a matter of fact, the is no events when operating any PMDG switch, except for NAV lights and Beacon light, which I guess are P3d default events. does this it mean it's a dead end? is FSUIPC supposed to be able to capture Custom events at all?
Really appreciate you willingness to help!
Thank you,
Amine