For the new sonos app - specifically for the sonos amp - the amp sub controls (for third party subs - including switching on the third party sub or off and crossover frequency) cannot be found anywhere under settings or amp settings or sound settings.
I have read that some sonos users can see this but I certainly can't. I have submitted a diagnostics again for sonos to debug.
I also just updated the app moments ago (9th June'24)
The update still didn't fix this. Come on sonos - the old app had this flawlessly implemented - why is the new app so buggy?