Also, and please correct me if I am wrong. If someone is truly having a problem breathing, wouldn't saying "i can't breath" be very difficult for them. And wouldn't they also be gasping and trying to suck in air?
You would expect them to have some trouble speaking but the old adage of, "if you can speak, you can breathe" is not entirely true. The person will eventually lose the ability to speak but may well be able to verbalize their struggles for a time.
Fighting and claiming that you can't breathe is a tougher pill to swallow. However, Floyd did fight and then died of asphyxiation. He was probably having milder issues to begin with but as the fentanyl began taking effect, because he almost certainly swallowed a large dose as cops arrived, it killed him.