https://www.crossway.org/articles/who-were-the-nephilim-and-the-sons-of-god-and-daughters-of-man-genesis-6/

Here is Professor Duguid’s view of Gen. 6. 1-5 which concludes that the best position sees “the sons of God” as the righteous humans. I want to bolster his position by noting that Adam was indeed called a “son of God” in the Lukan passage.

My personal view is that these two groups were humans (the righteous and wicked who kept separate from each other). At a few instances, where individuals of each group paired, there was a recognition of the natural vigor of their offspring. This was the discovery of hybridization. Wherever crops or animals are bred today, hybridization plays a crucial role for economic reasons.

I take it that some of these early humans wanted to assert their own way against God’s principles and create what they wanted: personal power. They were acting out the devil’s promise: “you will be like God” (Gen. 3.5). Humans playing God is only a temporary thing however, and will meet in judgment, both in this life and the next.