What did the last 'Arḍah (recitation) abrogate: the seven الأحرف (modes of recitation), or some verses, or something else? And were the readings of some Companions abrogated by it, or by the compilation of 'Uthmān?

Ibn Kathir mentioned that the annual recitation of the Quran by the Prophet and Jibreel (Gabriel) during Ramadan was for the purpose of affirming what had been revealed and preserving it. This continued until the last year of the Prophet's life, when Jibreel recited it with him twice. Uthman then compiled the Imam Mus'haf (the standard copy of the Quran) based on this final recitation. Some narrations indicate that this final recitation included a clarification of what was abrogated and what was not abrogated from the Quran, and that the widely circulated reading today is that which was established in that recitation. The Companions unanimously agreed upon what was confirmed from the Quran therein, and they abandoned what was other than it, although it is not possible to detail everything that was abandoned.