First: Floyd allegedly had enough opioid (heroin or fentanyl) in his system to kill "four men". This argument is touted by people who know perfectly well that the human body develops indefinite tolerance to opiates. There is no "enough to kill four men" in a regular user, as Floyd was.
You don’t say whether he had enough fentanyl in his system to kill him. Are you a medical expert? The point is he had a lot of fentanyl in his system. That he might have died from a fentanyl overdose, as thousands do each year, is potentially reasonable doubt whether Chauvin’s actions were the proximate cause of death. The legal standard of causing death is critical.