Your computer was unable to connect to the remote computer

I'm Having this AVD issue with a new workspace that was setup. It's a SessionDesktop application with a hostpool.  The Web version of the client works fine, can connect and open RDP session but the Windows App will not work either on-prem or off-prem showing the error in the title when attempting to launch the session.  I have tried playing with every setting I can find from RDP Properties, to Network ones, RDP shortpath, Entra SSO, Cred SSP, etc. Even if there was some sort of on-prem network issue it should still work when off-prem and it doesn't. But the web client works fine so I can't figure out what would cause this. The Application is just "SessionDesktop" and has no configurable parameters other than Display Name. The Host Pool has a private endpoint and when attempting to launch from the Windows App I can see some traffic going through our firewalls between the app and the PE as well as a few FQND's like windows365.microsoft.com, xxx.rdweb-g-us-r0-wvd.microsoft.com, xxx.afdfp-rdgateway-r0.wvd.microsoft.com etc... It's all 443 traffic though, no 3389 or 3390.

Entra logs show successful auth to Windows App and Conditional Access Policy result is Success with Grant Controls Satisfied and Session Controls Enforced.

I have the Windows App version 2.0.918.0 with Client version 1.2.6876.0 which should be the latest at the time of this writing. I tried the old deprecated RemoteDesktop app and it does the same thing.

One other thing I tried was downloading the. rdpw file from the web client and adding a bunch of parameters to the RDP advanced config like gatewayusagemethod, gatewaybrokeringtype, wvd endpoint pool etc. as they don't seem to be in there by default but it had no effect. I suspect those properties should be dynamically added at runtime rather than baked in to the config.

Any help would be appreciated.

Thanks.