See the link on here
https://www.easa.europa.eu/brexit-negotiations , referring to a "NOTICE TO STAKEHOLDERS - WITHDRAWAL OF THE UNITED KINGDOM AND EU AVIATION SAFETY RULES" on the European Commission website, which says:
Certificates issued before the withdrawal date by the competent authorities of the United Kingdom on the basis of the provisions of the Basic Regulation and its implementing rules will no longer be valid as of the withdrawal date in the EU. This concerns in particular:
Certificates of airworthiness, restricted certificates of airworthiness, permits to fly, approvals of organisations responsible for the maintenance of products, parts and appliances, approvals for organisations responsible for the manufacture of products, parts and appliances, approvals for maintenance training organisations, and certificates for personnel responsible for the release of a product, part or appliance after maintenance, issued pursuant to Article 5 of the Basic Regulation;
Pilot licences, pilot medical certificates, certificates for pilot training organisations, certificates for aero-medical centres, certificates for flight simulation training devices, certificates for persons responsible for providing flight training, flight simulation training or assessing pilots' skill, and certificates for aero medical examiners, issued pursuant to Article 7 of the Basic Regulation;
Certificates for air operators and attestations for the cabin crew, issued pursuant to Article 8 of the Basic Regulation;
Certificates for aerodromes, certificates for ATM/ANS providers, licences and medical certificates for air traffic controllers, certificates for air traffic controller training organisations, certificates for aero medical centres and aero medical examiners responsible for air traffic controllers, certificates for persons
etc