In any other case, the lethal levels of fentanyl would raise a reasonable doubt as to whether Chauvin's restraint killed Floyd. Fentanyl is a respiratory depressant - it interferes with a user's ability to breathe. Floyd was showing signs of fentanyl overdose before he was restrained.
Not just reasonable doubt - there would never have been charges filed in the first place. The symptoms are classic opioid overdose and the test corroborates it. That's what George Floyd died of.
I know so many people will be outraged at this attempt to deprive them of their moral dudgeon. They'd much rather it be a race murder so they can go on their own rampages, whether physical or verbal. But it is what it is, an OD, and that's all.