The "not-behind-the-paywall-and-NDA" GDK version is severely more limited than the invite-only GDKX.

IIRC the homebrew you can run is mostly UWP stuff? But if you want to launch a _game_, built for an Xbox, it requires to be in the program.

No it was quite different (again, unless they changed it? They might've, I'm long out of this scene). UWP apps had a lot more restrictions on them, the SDK was different, and you didn't have the full consoles hardware to use, compared to the "behind the NDA" SDK: it'd run slower, basically.

Still great, and good enough for most use cases