I appreciate that you want this to work, think it should work, and believe you’ve proven that it does work.
Google’s published support for the Chromecast Ultra is Level 4.2.
I’ve agreed at least once, perhaps twice, and I’ll do so again. It would be nice if Plex provided the ability to disregard Level.
@ChuckPA has commented elsewhere about how device profiles work. This is what I was describing previously. The baseline profile on the PMS can be overridden by the device. In general that’s the expected behavior - the device tells Plex what it supports.
Per that description, it sounds like the Chromecast Ultra is being queried for what it supports. (Which I believe is Google’s guidance for integrations.)
Edit: Additional comments about how base + capability augmentation operates:
chromcast ultra - chromecast.xml github repo - #8 by duncanbeevers
Similarly, even Emby folks have stated that the Chromecast Ultra reports that it is capable of 4.2:
Chromecast Ultra updated their codec support - General/Windows - Emby Community
