It’s not imposibile, it’s unlikely, and would be noticeable.
Dunno how app permissions prove that they are always listening when those permissions are required to access the mic at any point in time, including when you’re using the app and invoke it yourself.
Meta is plugging in USBs or connecting to people’s accounts en masse to get into people’s encrypted backups? I think not.
People keep claiming Meta does this, does that when it comes to microphones. Where is the proof? I haven’t seen a SINGLE piece of evidence to show that Meta is listening to you at all times when you aren’t using the app.
I only ever see people’s anecdotes of “it heard me talk about something cause it popped up later”.