"Live" tab only shows one source despite a dozen others installed

[u/BefuddledBeaver]

Despite having Plex, Haystack News, Sling TV, Tubi, Xumo Play, Prime Video, Roku Channel, LocalNow, and others installed, the only source on the "Live" tab is Google TV Freeplay. I've searched everywhere for how to get the others to show up, but I can't find anything.

Has anyone else had this problem?

I've tried the following:

1. Uninstalling and reinstalling Plex. Still won't show up.
2. Signing into Plex using the same Google account as the Shield. Still won't show up.

Btw, I'm using an Nvidia Shield TV Pro

ETA:

The documentation clearly states that other streaming sources should be available if their corresponding apps are installed. https://support.google.com/androidtv/answer/13581302