This is desperately short on explanation? The very high granularity suggests that some features are more privacy-invasive than others, but not why that is.
While come January the UK won't be part of the EEA, at least initially GDPR will continue to apply as most EU law has been grandfathered into UK law post-transition.
Yes, but as far as I'm aware the question of whether the UK will be a "third country" for purposes of data transfer outside the EU after January 1 is still undecided?
(Where is Facebook's data center anyway, is it Ireland?)
The UK is subject to EU law and is part of the EEA today; they have to go on what's true now, not what may be true in a few weeks. In any case the UK will inherit most EU data protection rules; they'll presumably change the wording in January, but the rules won't change.