Case T-218/18: Judgment of the General Court of 19 May 2021 — Deutsche Lufthansa v Commission (State aid — Aviation sector — Operational aid granted by Germany to Frankfurt-Hahn airport — Decision not to raise objections — Action for annulment — Status as an interested party — Safeguard of procedural rights — Admissibility — Guidelines on aid in the aviation sector — Doubts as to the compatibility of the aid with the internal market — Article 4(4) of Regulation (EU) 2015/1589 — Serious difficulties)