Very interesting! I didn’t know there was a Coptic language; it must be based on ancient Egyptian of course. Wonder if it has been utilized to help decipher hieroglyphics, or did that require the discovery of the Rosetta Stone?
And there was a Jewish Diaspora long before the destruction of the Temple in 70 A.D. Mentioned in Scripture when the Apostles addressed Jews assembled in Jerusalem from all over the known world, each foreign Jew hearing them in his own language.
Modern Egyptians claim to possess a unique national identity within the Arab world, your description of Egypt’s ethnic history helps to explain that.
The Coptic script was used by the early Egyptian Christians (much easier to learn the Coptic alphabet than the Demotic Egyptian script, which did not completely die out until about the 5th century of the Christian era), and Coptic is still used as a liturgical language by the Coptic Church. The use of Coptic as a spoken language in daily life seems to have died out about the 17th century.
Coptic has a lot of loanwords taken from Greek (which was widely spoken in Ptolemaic and Roman Egypt) but it did play a role in the decipherment of the earlier Egyptian scripts.