@Robertoevans,
Strange, I just updated to iOS 18.1 on both iPhone and iPad and the Sonos App and devices are working fine here. I’d perhaps give Sonos Support a call. Here’s the link to contact them…

https://support.sonos.com/s/contact

Maybe it’s something else that’s running on your iDevice, or local network, that’s causing the issue?

I’ve just got off the phone to my Son at his Home and he’s running iOS 18.1 too with his Sonos setup and that’s working okay aswell, so I don’t think it’s the recent iOS update that’s causing the issue you’re encountering here.

The mobile app is still janky on any version of iOS.

Use the desktop app or third party, Sonos are taking their sweet time in fixing the mobile app.

According to Nick Millington, Sonos Chief Innovation Officer, The new Sonos App is now equal to, or exceeds, the old S2 App in these 5 key areas…

• Add Product/Setup Success Rate
• System not found & Products not found errors
• Configuring stereo pairs and home theater
• App responsiveness
• Crash free sessions

See link:

https://support.sonos.com/en-us/article/the-new-sonos-app-and-future-feature-updates

These jokers also said the new app had feature parity when the new app released. GTFOH with this nonsense, can’t believe the crap they say. 
 

The new app is getting better but it’s still a buggy pos in my experience 

After updating to 18.1 Sonos is just crazy….slow, do not react to commands, lost of contact, impossible to shut down in a regular way…..