Odd, since the indexing occurs at the speaker level, and not in the controller running on the Mac. Perhaps you might try a reboot of your Sonos speakers, and then, if that doesn’t fix it, submit a system diagnostic within 10 minutes of recreating this crash, and call Sonos Support to discuss it.
There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.
When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your Sonos system and network.
It is not the indexing that is hanging. It is the S1 controller app that hangs after the popup to confirm the indexing (the popup stays on the screen and the app becomes unresponsive. The only way to exit the app is with a force close). The indexing on the sonos device does not start - so the problem is the client side application.
I can confirm that the S1 controller app on OS X running Big Sur and an intel processor works fine.
So it appears that either Sonos has not updated or tested for OX Monterey, or that the app does not work properly on the M1 chipset.
Then I’d recommend submitting a diagnostic from the M1 Mac and contacting Sonos support directly, so they can look at data in the log files, and see what is happening.