From 1st January 2021, EU law is incorporated into UK law but with the UK free to amend it, subject to any agreement to the contrary.
Previously the UK remained bound by EU law during an ‘implementation period’ lasting until 31st December 2020. Even after that date though, for the time being the UK courts are still likely to follow EU law and EU Court decisions to a very large extent, and are often required to follow them: see Brexit page.
GDPR, with minor amendments, continues to have effect in the UK as UK GDPR. Under the UK-EU Trade Agreement, data flows to the UK from the EU and EEA continue to be allowed for a further 4-6 month bridge period while the EU Commission considers whether to give an adequacy determination in favour of the UK. However businesses should be prepared for the possibility that there may be no adequacy determination: see GDPR: Brexit.