Hello ​@Scott M Decker, welcome back!

Sonos wants to update to 90.0-67171.

Has anyone still on S1 applied this update? Any benefit or detriment to updating?

Sonos S1 systems should not be able to receive this update. Sounds like the Sonos App has detected an S2 system or a Sonos product that is capable to be updated to the latest Sonos App version (S2).

If you’ve purchased any S2-capable Sonos products, you might need to power them off temporarily and then Reset the Sonos app and reconnect to your Sonos S1 App.

Let us know if the above helped and if you’ve had something changed in regards to your Sonos system.

It appears I was mistaken. 

Sonos_90.0-67171.exe is the latest (S2 only?) Controller for PC available but when I used the built-in update feature my S1 Controller for PC updated to 11.15.6

This type of confusion would be avoided if Sonos maintained proper release notes for S2 AND S1...