This is really a FAQ, it has been discussed so many times in the forum, and of course the manual has an highlight in blue to explain this. NOTHING in GSX controls or change the way jetways operates in a scenery.
- If a scenery doesn't have animated jetways to begin with, installing GSX won't change that, they will continue to be static.
- If a scenery uses the default FSX animation system for jetways, they will still operate as they were before, using the CTRL+J key, and installing GSX won't change anything the way they work.
The ONLY reason for having the "Parking has a jetway" option is to let GSX know there is a jetway there, so it won't try to create front stairs or call a passenger bus when boarding/deboarding passengers. Normally, if the jetway is listed as such in the scenery AFCAD, the flag is enabled automatically, because GSX read it from the AFCAD file.
But if your scenery doesn't have a jetway flagged as such in the AFCAD, maybe because it uses a static one, you will have to enable it manually, because GSX couldn't detect something that doesn't exists, but it will still need to prevent front stairs or the bus to be used. So, the only case where you need to enabled it manually, is when using 3rd party sceneries using static jetways, but it won't magically animate a static jetway, the only thing it will do, is to prevent the creation of front stairs and the passenger bus.
Basically, nothing in GSX ever changes or affects how jetways works (or not work) on any given scenery.
This is *somewhat* different is the scenery uses SODE jetways. In this case, GSX and SODE will cooperate, so GSX will know about the SODE jetways (even if they don't exists in the AFCAD, which is normal), SODE will be able to use the airplane door configuration from GSX and GSX will be able to control SODE from its own menu.