Strattic sites now support HTTP/3 by default! (No need to enable anything)
HTTP/3 affects how web browsers and servers communicate, with significant upgrades for user experience, including performance, reliability, and security.
You can see HTTP/3 enabled for your site in the Network tab in Chrome Dev Tools:
The way that it works is that the first connection uses HTTP/2 and if the response has the alt-svc: h3 header, then subsequents requests will use HTTP/3.