Linux

Did you double check that you are outputting to the correct device?

Might have switched to an output you don’t have connected like HDMI or something.

Restart, and if that doesn't work, sleep on the issue and it will magically fix itself when you wake up. Software is weird like that.

For a more serious answer, they might have accidentally uninstalled PipeWire or PulseAudio (the audio things needed for audio to play). I've done that myself before, and you can fix it by reinstalling it. If that's not the issue, see some of the other answers others have mentioned! There's a lot of good ones in there

Problem nearly as old as Linux itself:

My suggestion is to try pulse audio volume control (pavucontrol), you get a pretty decent number of options to look through and troubleshoot, in case it's routing to non-existent display monitor speakers or like a separate headphone jack instead of Lineout, etc.

I had a similar problem and it turned out to be a setting in my KDE Mixer. I wish I could remember exactly which one.

My suggestion, check every setting in the mixer, especially around outputs, slowly and carefully. Try each output one at a time if you aren't sure which is the right setting.

Does it happen under gnome, or kde with a different user?

Unfortunately these issues are really hard to troubleshoot. Personally if it works under another user, I'd start clearing user configs.

Maybe a sample rate mismatch somewhere?

Given your emphasis on rooms, am I correct to assume that you have a multi room setup realised via bluetooth or something?