I don't think you're understanding correctly. It doesn't even allow link aggregators such as link tree, on posts or bios.

I didn't talk about those but deep links to Facebook or Instagram posts. If I'm no mistaken those are authorized.

It seems like it's not allowed, otherwise the policy is way too easy to circumvent.

Musk refers to it as "free promotion of social media platforms", he's taking it personally. Personally I think they should all respond in kind.

It's not clear to me what will constitute promotion vs cross-linking. I'd avoid any links for now until Twitter's enforcement rules become clear.