I'll have to ask my friend about this...he was using SSL and had no referrers and they killed his account. He had no referrer policy tag. I know he was using a tracking script that he redirected traffic through as well, perhaps that was Http.
The HackerNews repo is gone (and thus the issue), but at one point this was a Github issue I successfully filed to get HN to add it so their referral data for non-SSL pages wouldn't be lost:
Since HN is using HTTPS, this should be very easy to test by just clicking on this link: https://www.whatismyreferer.com/
Note that HN includes this line of HTML which affects the sent Referrer header: