@jnelly,
I do still ‘suspect’ (personally speaking), that there is perhaps an issue with the MAC M1 here. It is a device that does seem to have Airplay issues reported by folk online, as mentioned earlier.
My betting is all your Sonos devices may Airplay fine with an iPhone/iPad (perhaps?) and that may go someway to show its likely a MAC issue, to then maybe chase up with Apple Support.
I think if it was a Sonos issue, there would be many more mentioning the issue here in the community with a variety of different Airplay sending devices.. but of course I can only guess that maybe the case at this moment in time.
Maybe Apple Support, or their user community can offer some further suggestions to try - it might just be a network/security setting on the MAC than needs changing, perhaps 🤔?