Yes and, at the same time practical support within programming language standard libraries & common tooling lags way behind: https://httptoolkit.com/blog/http3-quic-open-source-support-...

You will get most of the benefits of HTTP 3 even if your app libraries run HTTP 1.1, as long as the app is behind a reverse proxy that speaks HTTP 3.

Yep, for example, Caddy (zero special configuration to enable HTTP 3)