I just got done installing caddy 2.6 and can verify that it is in fact using quic (udp 443), and that it seems to be working well. One thing that I noticed is that ALL the stuff is encrypted. Which is the way quic is supposed to be. So I found a nice writeup on f5 on how to save the keys with the browser.
This is very nice, and it allows me to use wireshark to decode things. Just follow the directions in the howto. You might have to do some special things with quic. Futher blogs to follow.