Joint Cases T-639/14 RENV, T-352/15 and T-740/17: Judgment of the General Court of 22 September 2021 — DEI v Commission (State aid — Tariff for electricity supply — Fixing of the tariff invoiced to Alouminion by decision of an arbitration tribunal — Decision to take no further action on the complaint — Decision finding that there is no aid — Act open to challenge — Interested person status — Interest in bringing proceedings — Locus standi — Admissibility — Imputability to the State — Advantage — Private operator principle — Serious difficulties)