Note I said "possible". Your link specifically states "During the transition period the GDPR will continue to apply in the UK".

That said, apparently they've just reached a deal, and the transition period ends in 7 days, so lets see what they decided about with data protection.

Most EU laws are getting grandfathered in post Brexit, but the UK reserves the right to change them whenever they want. In essence, they've branched off their legal code from the EU bramch and can now commit changes to their orivate UK-only branch.

GDPR rights will most likely get eroded in the UK.