Ietf - HTTP/3 Explained
The QUIC working group that was established to standardize the protocol within the IETF quickly decided that the QUIC protocol should be able to transfer other protocols than “just” HTTP. Google-QUIC only ever transported HTTP - in practice it transported what was effectively HTTP/2 frames, using the HTTP/2 frame syntax.
While the work on IETF-QUIC has progressed, the Google team has incorporated details from the IETF version and has started to slowly progress their version of the protocol towards what the IETF version might become. Google has continued using their version of QUIC in their browser and services.
have decided to focus on the IETF version and are not compatible with the Google version.