All “Plex Experience Preview” builds have been removed from TestFlight, so none are listed on AppleTV at this point (which was confusing to me). It’s been announced here.
The β for the regular version of TestFlight had expired, so the situation was the same: no build listed, and installed apps didn’t launch at all.
It might have been corrected just now though: I got a notification a new build was avilable that supported AppleTV. I’ll check when I get back home, but it might be back!
In any case, the instructions to find the new β builds are listed here.
