I'm talking from either Gnome Shell, or any other desktop environment. I can already cast from Chrome, but I'd like to cast the entire desktop + audio (if possible), without Chrome.
71 Answer
With Chrome:
cast the entire desktop + audio is not very clear. (Does that mean mirroring? Or just access the files as with a file manager? It seems you tried that with Chrome but that Chrome doesn't play files with audio.)
Chrome can browse folders and files (open a folder in it). With Ctrl-O it can select files to open. Audio files and some video files (mp4) can be played in Chrome and cast.
Maybe accessing folders with Chrome and casting that is a solution.
(Oddly, at some point there was no sound in Chrome on the PC for local files, but there was when casting on the TV. That may be a solution to the problem you suggested, that there is no sound in Chrome for local audio files. When completely disconnected from chromecast devices - after a restart - Chrome was able to play audio on the laptop too.)
Without Chrome:
To cast video or audio files the simplest way is VLC. Connecting the PC to the same network (Wifi), your chromecasting device should appear in VLC under Playback - Renderer. (From one of the comments you seem to be looking for audio-only? VLC does it.)
For the whole desktop, a Gnome solution available on Flathub is GNOME Network Displays. (Cannot confirm it will work though, I'm in Kubuntu.)
