Case C-277/20: Judgment of the Court (First Chamber) of 9 September 2021 (request for a preliminary ruling from the Oberster Gerichtshof — Austria) — Proceedings brought by UM (Reference for a preliminary ruling — Judicial cooperation in civil matters — Succession — Regulation (EU) No 650/2012 — Article 3(1)(b) — Concept of ‘agreement as to succession’ — Scope — Contract transferring ownership mortis causa — Article 83(2) — Choice of applicable law — Transitional provisions)