Case C-388/19: Judgment of the Court (First Chamber) of 18 March 2021 (request for a preliminary ruling from the Tribunal Arbitral Tributário (Centro de Arbitragem Administrativa — CAAD) — Portugal) — MK v Autoridade Tributária e Aduaneira (Reference for a preliminary ruling — Direct taxation — Tax on capital gains from immovable property — Free movement of capital — Basis for assessment of tax — Discrimination — Option to be taxed according to the same arrangements as residents — Compliance with EU law)