Given that browsers discourage HTTP traffic (warning that the connection is insecure), given how easily free SSL certificates are available, and given that HTTPS is already the standard on small hobbyist sites, I don't expect The requirement for an SSL certificate has been a blocker in HTTP/3 adoption.
Do browsers warn for http (beyond the address bar icon)? I don't think they ever have for my personal site. I also don't think you can really say there's a "standard" for how hobbyists do things. I'm definitely in the bucket of people who use http because browsers throw up scary warnings if you use a self-signed cert, and scary warnings aren't grandma friendly when I want to send photos of the kids. The benefit of TLS isn't worth setting up publicly signed certs to me, and I don't want to invite the extra traffic by appearing on a CT log.
Like the other poster said, it all makes sense for the corporate web. Not so much for the human web. For humans, self-signed certs with automatic TOFU makes sense, but browsers are controlled by and made for the corporate web.
