Case C-562/19 P: Judgment of the Court (Grand Chamber) of 16 March 2021 — European Commission v Republic of Poland, Hungary (Appeal — Article 107(1) TFEU — State aid — Polish tax on the retail sector — Article 108(2) TFEU — Decision to initiate the formal investigation procedure — Information used to determine the reference system — Progressivity of rates — Existence of a selective advantage — Burden of proof)