‘All the fixes’ isn’t very descriptive to most of us, since we really don’t know which fixes you actually have tried. 
 

Which Sonos devices do you have?

How is your Sonos system connected to your LAN?

Which Sonos OS are you running on your Sonos?

Which router are you using?

What error is the Windows 11 machine providing?

What source of music are you trying to stream? 

Have you read the information in this thread?

What did Sonos tell you when you called Sonos Support directly to discuss it?

I have a 1, Play 3, Play 5, Beam,and Move.  I was using the old version of the web app because the new version didn’t work with my devices.  Oh and that’s yet another needlessly aggravating thing.  Why is the new app not compatible with older devices????    My router is a superfast Netgear Nighthawk hard wired to a Play 3.  My web app can’t connect to my Sonos system.  This problem appeared out of the blue for no apparent reason, I’ve followed the on screen instructions for this to no avail, the app on my Windows 10 laptop is working fine.   I haven’t called sonos support yet, just trying to find some way to make it work like it did 3 days ago.

What web app? Everything I’ve seen suggests the S2 web app will be released next week. 

I have the S1 app on my windows 11 desktop and out of the blue it suddenly couldn’t connect with my system.   That same app works fine on my windows 10 laptop.

Ok, so, not a web app, but the Sonos S1 windows app. The only reason I can think of for it to stop working on one machine, but continue working on another is the possibility of something blocking the ability of that computer to reach the speakers, which implies some sort of VPN, port blocking, or even a ‘work profile’, which often includes one or both of those. Have you tried to submit a system diagnostic, and call Sonos Support to discuss it? Even if you can’t submit that diagnostic from the Win 11 machine, I’d definitely call in to get assistance in diagnosing why one machine works, and the other doesn’t. 
 

Make sure your network is marked as Private to Windows: if its Public it will not work for Sonos.

Also check any anti-virus as they often force networks into “untrusted” mode which has the same affect.

I had this same problem, sonos opens but stays minimized, I can play and pause but never opens all the way up. the web app did work