Because physical force was being used at the moment of death, other medical factors don't absolve the police of responsibility.
Floyd died while the cop was kneeling on his neck, regardless of the actual cause. If he did indeed die from unrelated causes, then that's the officer's bad luck.
As another poster pointed out, shooting someone who has jumped from the Golden Gate bridge makes you a murderer, even if the ME rules that they died from the fall.
I have no interest in debating you - so will drop the back and forth, as I suspect you have a fixed opinion. I don’t.