Case T-166/21: Judgment of the General Court of 20 December 2023 — Autorità di sistema portuale del Mar Ligure occidentale and Others v Commission (State aid — Taxation of port authorities in Italy — Exemption from corporate income tax — Decision declaring aid incompatible with the internal market — Existing aid — Concept of ‘undertaking’ — Concept of ‘economic activity’ — Advantage — Selectivity — Distortion of competition — Effect on trade between Member States — Equal treatment)