After upgrading to Fedora Silverblue 34 beta from 33 I noticed that sound was coming out from both my laptop’s speakers and the headphones I plugged into it, which never happened before or with other distros. It turns out that Pipewire (or GNOME?) disables the auto-mute mode in ALSA whenever I plug or unplug my headphones, or when something first plays after a reboot.
There is an issue that’s at least related upstream, but there hasn’t been a response from the devs there, so I’m wondering if anyone has this issue as well, and whether anyone has a workaround for it. It is easy enough to enable the auto-mute mode via amixer -c 0 set 'Auto-Mute Mode' Enabled, but I have to redo that every time I plug my headphones in and/or after a reboot, and just setting it to run on login doesn’t work since it gets turned off when a sound first plays.
The real trouble is that if I have my headphones on and I’m playing something I won’t notice that it’s also playing through the speakers unless I remember to check, and the only reason I’m even using the headphones is so the sound won’t bother anyone else.