Hello,
This issue cannot be solved with general troubleshooting steps.
We could check if there's any error message in your eventlog (RDS server)
When we troubleshoot such an issue, we can always try to connect to RD server first.
If you can connect to RD server via "mstsc" , the issue should be on the connection broker or web/remote app, you only need to confirm logs on such servers.
If the Answer is helpful, please click "Accept Answer" and upvote it.