[dsp]

> DNS over HTTPS uses TCP-based http/2

DoH (ietf rfc 8484) recommends http/2 as a minimum, http/3 is a valid DoH transport.

> which is less efficient

What kind of efficiency are you referencing? This is not a clear cut issue.

> UDP-based QUIC (aka http/3)

The linked rfc uses only the quic transport, not http/3.