So, as of now it is not completely clear, however, in may, Netanyahu claimed in a interview with former US Advisor Dan Senor that out of the 30,000 casualties at the time, 14,000 were combatants and 16,000 were civilians. (
https://time.com/6979208/israel-gaza-death-toll/) Now, it may be different now, but I see this claim of 80% as being likely misinformation. Also, I have not found this claim repeated anywhere besides Israeli news sources, which have the potential to be heavily biased.