Yes I noticed that A9 wasn't on the list. But I'm strongly inclined to think the issue is your interface. Maybe it needs to be updated.
This gets into the weeds a little, but
Module 19 - Gateway has a master list of the other modules installed in your car. Some interfaces will look at that master list, and give you a list of
only the modules in that list... instead of the full list (that shows when you scroll in your video).
Alternatively, the interface can "scan" the car to see what modules are available. And then, again, the list would
only show those modules.
The list you scrolled through seems to have almost every module that's available on VAG cars (except A9, as we know). But I know that several of those modules are not installed in your car, or any Golf model. So that tells me your interface is not "scanning" the car or checking the master list in Module 19.
Assuming the wiring to your soundaktor is good, including power, then a properly working interface should see it. If you are only curious about the soundaktor but you are otherwise happy with your current interface then you might be at a stopping point.
But, I would very very very strongly recommend VCDS or OBDEleven. Both are vastly more capable than any generic interface. Both have great official support forums and support on other forums like here. I prefer VCDS myself, but either will get you sorted. No need to buy credits with OBD, and no credit system at all with VCDS.