It will get whatever it can. You also don’t need a mapped port, Aether can punch holes through firewalls via reverse-opens. (Though having a port open will significantly increase your connection speed and frequency.)

You can look at the port it chooses through netstat, it does not have a fixed port. However, once it gets a working one, it won’t change it from then on so you can map that port.

Edit: you can, but it having an Electron shell for UI (the actual app is Go) makes the build process somewhat complicated. It’s on GitHub though, feel free to take a look at the makefile and give it a shot.