Was Moses king of Ethiopia for forty years?

No. Moses was the (adopted) son of a pharaoh’s daughter in Egypt for forty years (Acts 7:21,23), a shepherd in Midian for forty years (Ex. 3:1; Acts 7:30), and the leader of the children of Israel in Egypt and the wilderness for the rest of his life (see Ex. 3 to Deut. 34), but never the king of Ethiopia.