Need assistance with GTN not loading

You can't write this dataref. However it tells you how many aircraft are active in XP11 (including yours).

Either you set XP11 AI traffic to something and you'll see them around you, and their number in the dataref.

Otherwise you use a 3rd party plugin injecting traffic the modern way (using the new TCAS datarefs) and you'll get the same effects (around you + number).

Using a 3rd party plugin overriding traffic the older way won't work in XP11.50, it is not supposed to.