Wireguard only supports UDP. The main reason being TCP over TCP is extremely slow.

You could try OpenVPN, I think that has a TCP mode though, as said, don’t expect good performance.

Try UDP port 123 sometimes that goes through the firewalls

For my setup, I used UDP port 443. For the vast majority of situations it works well as TCP 443 is for secure internet traffic. It seems admins often blanket 443 port open regardless of protocol 🙃

I’ve never tried this myself, but the docs have some ways of maybe getting into working https://www.wireguard.com/known-limitations/#tcp-mode .

The udp2raw repo has the following description:

A Tunnel which Turns UDP Traffic into Encrypted UDP/FakeTCP/ICMP Traffic by using Raw Socket,helps you Bypass UDP FireWalls(or Unstable UDP Environment)

As long as you’re certain your wireguard server works from other networks… You could use nginx as a proxy to have your server accept incoming traffic from UDP port 53 (DNS)… But, be careful!

I would strongly suggest you whitelist the retrictive network for use on UDP port 53. Is the WAN IP static on the restrictive network? Do you know the size of the WAN subnet? I’d try a quick test over UDP port 53 using nginx, then close it up. If it works, create your firewall rule to whitelist only the restrictive network and Bob’s your aunt.