Coptic, or as it is known in TTL Khemi, Masri and/or Egyptian
The Muslims conquer Alexandria from the Romans in 641 but there is no Roman counterattack and brief recapture of Alexandria TTL. The Muslim commander Amr ibn al-As successfully appeals to Caliph Umar to make Alexandria the provincial capital of Egypt as opposed to building a new capital in Fustat (what would become Cairo). The sub-provincial divisions, the nomes and pagi are preserved and re-dubbed khittas, allotted to companies based on tribal affiliation.
Alexandria's citizens are offered the choice to stay and pay the jizya or leave; those who leave are mostly Greeks. The Greek quarter is repopulated by a small military colony of Arabs who themselves are outnumbered by a migration of rural Egyptians from the surrounding villages and towns. Much like their Roman and Ptolemaic Greek predecessors, the Arabs are careful to maintain the distinction between Alexandria's communities. Arab presence in Egypt exists mainly in scattered estates which requires the need of educated Egyptians to help govern the land.
al-As and the governors following him attempt to encourage conversion to Islam with promises of land, money and titles. The Quran is even recited in the Egyptian language so it would be intelligible to all. The landed gentry were the first to be receptive to the new religion; it meant untold political power, land and prestige previously denied to them for centuries. The urban-dwellers followed soon after. Muslims would soon transform from a small minority in the seventh century into a plurality by the ninth century.
Although Egyptians increasingly adopted Islam, their distinct identity would be preserved and later revived. Arabs, Turks and Nubians in addition to native Egyptians would participate.
In response to the growing attempts at Arabization and political marginalization by the Ummayads, the Egyptians would join the countless non-Arab mawali communities in supporting the Abbasid usurpation of the Caliphate. A prominent noble named Thanasys al-Masri (Athanasius the Egyptian) led the final assault on the walls of the Ummayad capital Harran in 750. It was also al-Masri who discovered the Ummayad princeling Abd ar-Rahman and his Greek servant Bedr attempting to escape Palestine; they were returned to the Abbasid caliph who had them both executed. As gratitude, the Caliph would offer Thanasys the governorship of any land he desired; al-Masri requested Egypt.
The Thanasysids were the first native dynasty to rule Egypt since Nectanebo II. As such, they gave great care to Egyptian culture and language, sponsoring prominent Egyptian poets. Among them would be the famous court poet Mariam Al-Tayibatani who was born during this era and praised the Thanaysids as the true successors of ancient pharaohs like Ramses the Great, enlightened by Islam. She would assert the supposed cultural superiority of the Egyptians in philosophy, logic, astronomy, music and other subjects.