I cannot really help you, but with the freerdp client there is a similar/the same issue
Up to RDG 2016 it works, with RDG 2019 and 2022 the upload (from rdp client to server) is way too slow.
This only happens with RDG HTTP+websocket. If you have a Windows 8 client around, you will probably see that this is not affected.
I don't know if there is a way to disable RDG HTTP and enable RDG RPC only as that would probably solve your issue
When using a freerdp the option /gt:auto,no-websockets is your fix.
the funny thing is that 2016 has rdg+websocket, so it was not always broken. Don't know what Microsoft changed.