[logifail]

> In Facebook's case, there are permission levels you can set on posts, including a "public" option (which isn't actually public though and will require a login anyway, but it can be any login)

Q: Have you tried this?

In a private browser session I started at google.com, searched for "site:facebook.com nextgrid", picked some random post, click through, and was reading the post without anything other than seeing FB's cookie banner. No sign of any login (which is good 'cause I don't have one)

[Nextgrid]

I suspect it depends on your region, page/post in question and browser fingerprint. A post marked as public isn't 100% guaranteed to be publicly viewable. Sometimes you can view it but merely scrolling down on the page would trigger a login form for example (I've had this happen for pages that are definitely meant to be public such as businesses who'd have an interest in getting as many eyeballs as possible on their content).

I might be wrong and maybe the behavior is actually fully deterministic and isn't nefarious, but knowing the company behind it I'll assume malice until proven otherwise.