RDP connencton on a specific WAN

Hy everyone!

I have a HAPac. I’m trying to find a solution to create an RDP rule which uses a specific WAN.
Here is the thing.
Our ISP could not provide enough bandwith (but it’s stable) so next to this I want to use 4G too.
I would like to create a rule where only the RDP traffic goes through the ISP and anything else goes on 4G.

What steps would be the best guide in this case?

Thanks in advance!

How many users on the LAN are using RDP?

Incomming RDP ?
Where Client via the Internet connects to PC’s and Server’s
in your Local Network

or Outgoing RDP ?
Where the PC’s in your Local Network connect to
Server’s in the internet

I assumed outgoing from the LAN as he wants the router to ensure a specific WANIP is used.
If it was incoming he wouldnt need to do so as the incoming would be from external users in which case he would tell those external users to use a specific WANIP or domain name!
But agree its not clear!!!