I am having the same issue if anyone could shed light on how to get rid of this annoying prompt that would be great

This is an annoying and recurring problem with recent versions. They temporarily fixed it and then it came back. 
 

There have been so many minor version releases recently, so I’ve updated multiple times hoping they fixed it again (without breaking other things… ie when the volume control had zero numbers. Now it has numbers but it’s still more finicky to use than the old UI). 

Edited original test after testing:

I tested this shortcut in iPad by having BT off in the settings. Sonos app started and the prompt didn’t come and BT remained off in the settings. So to me the below shortcut worked ok in getting rid of at least the initial prompt that comes if BT isn’t on when starting Sonos app. 
 

If it does not give the prompt “mid running” then one workaround on iPhone could be to create a shortcut that has these actions:

1. Turn Bluetooth on
2. Open app (select Sonos)
3. Turn Bluetooth off

Then add the shortcut to Home Screen and use that to open the Sonos app.

Apple’s Shortcuts app is great. If you’re not familiar with it check https://support.apple.com/en-gb/guide/shortcuts/welcome/ios and YouTube channels like Proper Honest Tech for some ideas what to use it for. Install from App Store.

Did Sonos fix this