It would be easier if you had UiPath installed on that machine that you are RDPing into, then run it directly on the machine.
When UiPath sees the RDP window, it only sees the entire screen as one element, because RDP is an application, not a machine with elements. It can’t translate the elements that are being broadcasted through your RDP window as elements.
But, you can automate actions to the RDP session using Citrix automation, like Keystrokes and Image/OCR clicks. Although, not that reliable.
Another option you have is to set up your Powershell script to run on a specific machine and also perform all the actions you were wanting UiPath to do, so you can run it from your main machine and it will start on the other machine. However, this may require some higher level authorization (ie admin rights), and there is another learning curve to this as well.
I hope I answered your question atleast a little bit.