What are you trying to do?

Some networks block UDP traffic in specific ports in an effort to firewall VPN access. Mullvad exit nodes in Tailscale use port 51820, which is blocked in a few networks I use on my laptop.
The dedicated Mullvad VPN app supports setting the connection port to 53, which is the same as DNS, which gets around such firewalls, as they can't block port 53 without breaking DNS.

How should we solve this?

Add the ability to set the remote port on Mullvad exit nodes, either in-app or through the Admin console.

What is the impact of not solving this?

Mullvad exit nodes are completely unusable in networks with restrictive firewalls without a mechanism like this.

Anything else?

Mullvad mentions this capability in their app in passing in their FAQ when talking about a Comcast gateway: https://mullvad.net/en/help/faq/#71