Although I am using pycurl and not directly calling the libcurl API from C, I think this is the most appropriate place to report the bug. According to the documentation, only OpenSSL is supported. This uses the BoringSSL fork with the Quiche library for QUIC. I suspect that it could be a missing API in Quiche, but I'm not sure.

I did this

import pycurl
from pprint import pprint

TEST_URL = 'https://facebook.com'

def certinfo_demo(url=TEST_URL):
    c = pycurl.Curl()
    c.setopt(pycurl.URL, url)
    c.setopt(pycurl.WRITEFUNCTION, lambda x: None)
    c.setopt(pycurl.VERBOSE, True)
    c.setopt(pycurl.OPT_CERTINFO, True)
    c.setopt(pycurl.HTTP_VERSION, c.CURL_HTTP_VERSION_3)
    c.perform()
    return c.getinfo(pycurl.INFO_CERTINFO)

if '__main__' == __name__:
    pprint(certinfo_demo())

I expected the following

I expected it to print the certificate information. When the c.setopt(pycurl.HTTP_VERSION, c.CURL_HTTP_VERSION_3) line is removed, it works fine. I was using a local test server but replace it with Facebook to make it reproducible. It prints an empty list when using HTTP/3.

curl/libcurl version

PycURL/7.45.1 libcurl/7.86.0-DEV BoringSSL quiche/0.14.0

operating system

Fedora Linux 36, in a Python venv