Un the 620s the Arabs were not “Muslim” when they conquered the Ummayyad empire. Islam o Ky was created later in the 700s by the Abbassid dynasty.
The arabs took over lands without slaughter. In Egypt they were aided by the local Egyptians and Jews. Even as recently as the 12th century, the majority of Egyptians were Christians, but that changed with the Mamluks
Funny how all scholars and even muslims claim different. They all must be grossly mistaken and bow to your vast historical knowledge.