Nephillim spoken of in the Bible existed . That’s why a command was ordered to kill them all before and after the flood

They where before the flood.. and they made a return after the flood and the Hebrews where brought out of Egypt on a mission to destroy the giants the sons of Anak...

(Numbers 13:33) "And there we saw the giants, the sons of Anak, which come of the giants: and we were in our own sight as grasshoppers, and so we were in their sight."