Required reviewers I think means in a team of [A, B, C], (A | B) are required but not C.

Unless i’m missing something, it should not be the same as “administrators” - otherwise branch protection rules would be fine.

That's odd, https://github.com/pricing mentions it as a paid option.

A feature that's available for free on public repos isn't necessarily free for private repos, it seems. The wording on the pricing page isn't very clear about this, though.

If they mean that they're now removing required reviewers for public repos in the free plan, that's definitely a big step backward I think.