There is not. You could compile the HTTP/3 libs with the flag enabled and the link that library when you compile your browser with the appropriate flags (but th

There is not. You could compile the HTTP/3 libs with the flag enabled and the link that library when you compile your browser with the appropriate flags (but there's no sure thing this will be possible). And for 99.9999% of the people on the web their browser/user-agent will be unable to establish a connection to an HTTP/3 listening server that does not have a CA TLS cert. It's the worst aspect of HTTP/3. It makes all web things require CA TLS and means that if something in the TLS breaks (as it does every couple years with root cert expirations, version obsolecence, acme version obsolecence, etc) then the website is not accessible. Because there's no such thing as HTTP+HTTPS HTTP/3. There is only HTTPS. It's designed entirely around corporate/institutional needs and is a terrible protocol for human people. HTTP+HTTPS websites can last decades without admin work. HTTP/3 websites can only last a few years at most.