GDPR is still in force until the end of the transition period (I think Dec 31). What will change after then, who knows? I don't think I've seen anything coherent on any front from the government at this point.
This is the case for many EU laws - depending on the area [0], laws agreed upon in Brussels don't actually mean anything on their own, but member countries are required to write them into their own law. After Brexit happens such laws will still apply, as they have been written into UK law.