iPhone stuck on mute?

While I slept last night, it seems my phone decided that it should just remain muted forever. It reports correctly that the side switch is muting or unmuting it, but the sounds never re-activate. The alarm works correctly, so I know the speakers are functioning. It's simply acting as though it's been told to mute, without that actually being the case. Asking Siri to unmute the phone results in Siri saying (in text, because again, no sound) that the phone is already unmuted --- even when I actually do engage the mute switch on the side. I've tried power-cycling the phone to no avail.

Is this a bug?

This is an iPhone 12 Pro Max.