I don't care if he was on drugs, and he sure as shit didn't look like he was whacked on fentanyl or opiods. I was in a serious accident, dealt with years of debilitating chronic pain, and as such have extensive experience with very high doses of painkillers. The only time I would have had some respiratory distress while on pain meds was when the pain and dosage was so high that I was incapable of doing much of anything. In such a state you're not putting up a fight or a struggle, you're barely conscious.
You can vocalize to a point, while having your neck squeezed. I've always had a strong, thick neck, and if you flex the muscles in your neck, which you can see this guy doing, provided there isn't direct pressure to the windpipe, which there is not, one can vocalize. The knee wasn't directly on his larynx, it was on his carotid artery, the other artery would have been compressed against the pavement. Putting sideways pressure would have gradually constricted his windpipe, but pressure on the arteries is how you put someone out. Continued pressure is how you kill someone.
The guy is restrained, not moving, not struggling, and there are a couple instances in which the cop shifts his body and presses his full weight, sinking his knee into his neck. You can see his neck bend and sink to the pavement, not to mention the shock on his face. He was pleading while pressure was being applied, up to a point. The pressure on his neck 'appeared' to be an effort to silence him, which is a total power/control move. Lastly, I would bet this man was terrified in that moment, in light of so many other unjustified or questionable deaths of black men.
I am trying to be as charitable as possible, but any moron with training knows you should be careful when applying pressure to the neck. Furthermore, and this is the biggest point, the guy was handcuffed and on the ground. It is stupid simple to maintain control when someone's hands are cuffed behind their back and they are lying on the ground. There were two officers walking him when he went down, and then one decided to kneel on his neck?