Do I understand you correctly that the scenery is to fault here ?
So GSX does not recognise a single parking space at EDDK where I could park with the A330 ?
GSX just reads what's the scenery has set so yes, it seems the scenery is at fault here.
That is a bit confusing. According to this website, there are several parking areas in EDDK where an A330-900 could park. for example A11, A21, B11, B21 etc.
You are assuming the scenery matches the real world, which might not always be the case, and sometimes the way the sim works, make it impossible for developers to match the real world, for example:
A11 doesn't even exists in the scenery, it has markings painted, but it's not represented as a parking spot, because in real world is a MARS (Multiple Apron Ramp System), which is not supported by MSFS, which is why Aerosoft probably didn't depicted it. B11 and B21 are also both MARS positions, so they don't exist in the scenery
A21 has been set with a radius of 26m, so GSX correctly flags it as being too small for an A330-900, which has a Wingspan of 64 meters. This seems to be a mistake, because in this case the designer decided to have the MARS position ( the one for bigger planes ) in the airport file, so they used a different strategy than the other MARS locations where the ones for the smaller planes were included, but set it a too small radius, which should have been set to something like 35-40 mt, if the idea was to have at least one MARS location for large airplanes represented.
Unfortunately, none of them is shown as usable in GSX
That is correct, according to the information GSX is getting from the scenery.
Does this mean that I have to edit each parking space individually in GSX?
Now, it seem you haven't read my previous explanation carefully because, all the 3 points I quoted from the manual, the ones at Pages 11, 33 and 27, are all explaining why this is NOT a problem, and you can still USE those parking spots.
The only reason why you might want to edit the parking themselves, is so they wouldn't "look" as being "too small" and you won't get the warning from GSX, but that's about it, you can still USE them if you want without editing. Editing will basically remove the warning, that's it.
And my last point, which suggested to read Page 27 of the manual, which explained the "Ignore Wingspan when parking" global setting, is another way to deal with this, by basically telling GSX to stop care about the parking size *everywhere* you go.