No Sound In Flatpak Apps on Steam Deck

[foxing-quietly]

As per the previous discussion I am opening a new issue. Using my Steam Deck in game or desktop mode, I am unable to stream sound in flatpak applications added as non-steam games. This applies to emulators like Xemu, PCSX2, and everything else added through emudeck.

Here are my findings:

1. In gaming and desktop mode, I can use RemotePlayWhatever to stream native Linux and Proton-based steam games. Sound works fine.
2. I can do the same with non-steam games I've added to Steam as exes that get run through Proton. I can also add Linux native non-steam games to Steam and stream them. Sound works in both cases.
3. Any flatpak applications (games or otherwise) added to Steam as a non-steam game do not have sound when I stream them in either desktop or game mode. Any non-steam shortcut with the target "/usr/bin/flatpak" streams but without sound.
4. I have tried both the stable and beta Steam clients on the host and guest PC during streaming. No change reported.
5. There is no sound in the game mode menu or desktop unless I have a game playing.

Let me know if I can help in any other way.