NB. If using HTTP/2, then no UA header is needed. The examples I provided use HTTP/1.1

    curl --http1.1 --resolve lite.duckduckgo.com:443:52.142.124.215 -d "q=test" -A "" https://lite.duckduckgo.com/lite/

"Several characteristics of HTTP/2 provide an observer an opportunity to correlate actions of a single client or server over time. These include the value of settings, the manner in which flow-control windows are managed, the way priorities are allocated to streams, the timing of reactions to stimulus, and the handling of any features that are controlled by settings."

HTTP/2 has some fingerprinting enablers that HTTP/1.1 does not. The above is from the HTTP/2 RFC.

Further reading: https://www.blackhat.com/docs/eu-17/materials/eu-17-Shuster-...