Windows 8.1 and RDS 2019 not working

Hi,

I have an RDS environment, gateway, broker and session host. all on Windows 2019.

I can connect fine from a Windows 10 machine, however windows 8.1 just doesnt work, it authenticates with the RemoteApp web front end, but just doesnt make a successfull connection when launching the app. I see no errors, just tells me the server is unavailable. Is there an easy fix that I am missing? All servers and clients are fully up to date as they are all in Azure and have full internet access.

Thanks