It’s not clear to me what you’re trying to do in terms of network access.

So your “main Windows machine” is inside your local network, and you are accessing it remotely via RDP from outside your home, which you then use to control a Proxmox server? You didn’t have an open RDP port open to the internet before, right? What is your setup?

Why do Twingate and dynamic dns not work? What kinds of errors are you encountering? You could also try Tailscale.