Help has been receiving enquires about changes occurring after Brexit day which was yesterday. As far as we understand there is going to be very little change until the end of the transition period on 31st December 2020. Please see more details at UK Government site https://www.gov.uk/guidance/living-in-spain .
UK nationals living in Spain should follow previous advice which is get your residencia sorted and change your driving licence to a Spanish one. You can do this as before up to 31st December 2020. Failure to do this could have unintended consequences such as loss of healthcare rights and your UK pension may not be increased annually.