Windows RDS Web App Cannot Connect

I dont actually know where to ask this question - however.
I am trying to secure a Windows Remote Desktop Application server behind Cloudflare Zero Trust. I have the application created, and the tunnel working. I can successfully browse to the website, my Cloudflare policy works, etc., etc.
What doesn’t work are the apps - they only use port 443, so I dont see how there is any configuration change needed in Cloudflare, but maybe? I have tried a number of different changes on my RD Gateway - I keep hitting the same issue of the app not working.
If I remove all of the Cloudflare configuration then the RD Web Apps works again as expected - they just don’t work their the proxy/tunnel.
I am happy to provide more details on the troubleshooting I’ve done thus far, but what I was really hoping for was a little direction from someone who has set this up successfully.
I’ve seen lots of post and tutorials on getting just RDS to work, most of them require WARP, but I really just want RD Web Apps to work they way they are intended without any agent or end-point configuration.
Thanks in advance…

This is the error I get when launching an RD Web App
Remote Desktop Connection
The remote resource can’t be reached. Check your connection and try again or ask your network administrator for help.

[Expanded Information]
Error code: 0x300000d
Extended error code: 0x0