In terms of cultural continuity, the Copts trace back to 5th-century Roman Egypt, which was already a hybrid of ancient Egyptian, Hellenistic, and Roman cultures; while the Arab population traces back to the 7th-century Arab conquest. Both groups are pretty far removed from ancient Egypt, although the Coptic language does descend from Roman-era Demotic which in turn descends from ancient Egyptian.

In terms of genetic admixture, modern Egyptians are roughly 14% sub-Saharan African, 19% Maghrebi (these are the two “ancient Egyptian” groups, so the modern population has about 33% ancient ancestry), 37% European (this would be the Greeks and Romans who had become part of the population by the time the Copts arose), and 30% Middle Eastern (descended from post-Roman migrations). So broadly speaking, Copts are a two-way mix of ancient Egyptians with Greco-Romans, while non-Copts are a three-way mix of ancient Egyptians, Romans, and Arabs.