Case T-626/20: Judgment of the General Court of 21 December 2022 — Landwärme v Commission (State aid — Biogas market — Tax exemptions compensating for additional production costs — Decisions not to raise objections — Action for annulment — Interest in bringing proceedings — Admissibility — Failure to initiate the formal investigation procedure — Serious difficulties — Article 108(2) and (3) TFEU — Article 4(3) and (4) of Regulation (EU) 2015/1589 — Guidelines on State aid for environmental protection and energy 2014-2020 — Cumulation of aid — Aid granted by several Member States — Imported biogas — Principle of non-discrimination — Article 110 TFEU)