Video from Houseform Apologetics
"On the Spirits of Pre-flood Giants" -Dr. Michael Heiser
There are many things about our lives, our world and creation in general that God the Father choses not to reveal to us. Creation is complex beyond our cognitive ability to understand and also our sin corrupts our understanding. So God is wise in not telling us about many things. Yet much is alluded to in scripture and other sources about creation etc. by the human biblical authors.
One area of interest that is alluded to is Giants, the Nephilim and what became of them. Dr. Heiser discusses this briefly. For further reading see below.
Like everyone who disseminates anything to do with God's Word there are critics. If you go to any Christian Pastor, scholar old or new you will find criticisms. Dr. Heiser is nor different and you will find many who take another view or dismiss him as a heretic. Personally for what its worth my reading and studies of theses subjects over the years are clarified by Dr. Heiser's studies. No man is perfect and the Word of God is the final and ultimate source. Read for your self his books and there is a lot on the internet to read as well. Here is an example of some differing opinions: SOME CONCERNS WITH MICHAEL HEISER’S “THE UNSEEN REALM” (link)
I personally like to read opposing views to better help me understand the issues and subject. My reading of theses articles finds that the authors are reading something else into Heiser's scholarship, but that is may opinion. See what you think.
For further in depth reading: The Unseen Realm: Recovering the Supernatural Worldview of the Bible by Dr. Michael Heiser (link)
Dr. Micheal S. Heiser (link)