I wouldn't suggest WebTransport unless/until Safari gets support. Instead you can use WebRTC DataChannel today for UDP in all browsers. Also, WebTransport doesn't support direct P2P connections but WebRTC does.
I have ported Quake III to use DataChannel and it works great (once all the WebRTC boilerplate is in place). You can test it here: https://thelongestyard.link/ Once you click the multiplayer link you will get a URL with your server name, which others can visit to join your server instantly.
I have ported Quake III to use DataChannel and it works great (once all the WebRTC boilerplate is in place). You can test it here: https://thelongestyard.link/ Once you click the multiplayer link you will get a URL with your server name, which others can visit to join your server instantly.