Case T-653/22: Judgment of the General Court of 10 December 2025 – Silex v Commission (Research and technological development – Horizon 2020 Framework Programme for Research and Innovation (2014-2020) – Recovery of sums unduly paid under to a grant agreement – Challenge as to the validity of a contractual debt which has become final – Legal certainty – Inadmissible plea – Principle of good administration – Duty of diligence)