I did not buy it via the Market Place and it's resided in the "Official" MSFS 2020 sub-directory in my Steam folder. For some reason this airport is no longer being recognized by the sim in the "Official" directory
Well, there first obvious question is: if you haven't bought it on the Marketplace, what is doing in the Official folder ? The whole point of having a Community folder, which is read AFTER the whole Official folder, is precisely to reduce the change of being dependent on priorities for 3rd party airports.
So my question is: How can I get the GSX include/exclude behavior to work while the airport is in the "Community" sub-folder?
The only thing the GSX Config panel controls, is the Exclusion/Inclusion for GSX OWN jetway replacement files, and the rule is very simple:
do you have a 3rd party airport for that ICAO ? If yes, you MUST Disable the GSX jetways file, if no, you can keep it Enabled, unless you want to use default jetways there for some reason.
That's why any discussion about priorities and GSX jetway replacement files is not relevant when a 3rd party airport is involved: it doesn't matter, because GSX replacement files are not supposed to replace 3rd party airports, the only thing they do ( if present!! ) is to replace jetways at *default* airports, and they will always succeed to do that, because default airports are in the Official folder, and GSX files are in the Community folder, so they will always obtain an higher priority over the default airports package, just because they are in the Community folder.
The only possible problem might be if you have *another* scenery that also replaced jetways on a particular ICAO, which is also in the Community folder, and it got an higher priority than GSX, resulting in not seeing GSX replacement jetway for a *default* airport. But in case of a 3rd party airport, which you are always supposed to Disable from GSX in any case, this won't be a problem.