After having the same problem you two mentioned, I've reinstalled all he FSDT software and sceneries endless times, and even uninstalling my Avira antivirus and leaving only Windows Defender, I was able to solve it after seeing a comment on the forum (I don't remember the user but I'm glad lovely person you shared your solution that helped me), updating the P3Dv4.5 navigation database which I normally do with every AIRAC update called "World FSXP3D package" (created and constantly updated by Herve Sors, thank you very much for your great work) and there was an error in the version 2208 update (August 11, 2022) that caused the crash of "Couatl64_P3D.exe" when loading the flights, GSX 1 and 2 could never work due to that error, so I downloaded and installed the new version of "World FSXP3D package AIRAC 2208-R2" and it fixed my problem, hallelujah!
If you use that nav database update for your P3Dv4.5, I recommend that you install the new corrected version and it should fix the problem.
If you have already done so and the problem persists, you may need to exclude more EXE files and folders from FSDT to avoid errors; In case your problem persists, it would remain for FSDT to correct in detail any errors you are getting with the latest version of GSX (which by the way I have not updated after reading the number of issues it has presented when launching GSX Pro) .
Good luck and regards.