Chauvin died of a cardiac arrest. You've got that much right. A cardiac arrest happens (in this case, at least) due to ventricular arythmia of the heart. In this case what happened is that the toxic dose of fentanyl he had in his system depressed ( his brain's respiratory centre (this meant that the rate and volume of air he could inspire was reduced). He was not suffocated or asphyxiated by the pressure of Chauvin's knee on his neck. This meant that Floyd's heart was progressively starved of oxygen. When a human heart is deprived of adequate oxygen like this, it starts to beat in an irregular way (this is called arythmia). All opioid/opiate drugs: morphine, oxycodone, heroin, dihydromorphone, and -in this case- fentanyl, when taken in excessive doses cause this to happen. Once the ventricles of the heart go into arrythmia, the heart stops beating very quickly. This is called cardiac arrest and it is naturally fatal.
If you watch the video of Floyd's death, you will note that his is alive one moment and the next he just quietly loses consciousness - i.e. he suddenly dies of cardiac arrest. People who are choked/strangulated/asphyxiated do not die like that. Chauvin could not possibly have known that Floyd was about to die of a cardiac arrest due to ventricular arrythmia caused by the fact he had over-dosed on fentanyl (he also had "methyl amphetamine" in his system which would also certainly made his development of the fatal ventricular arrythmias more likey, esp when mixed with fentanyl).
In short, you say: If Floyd was DYING of cardiac arrest..." Death by cardiac arrest is not a PROCESS. Cardiac arrest happens "in a second;" i.e. your heart just suddenly stops beating and you are toast (unless you can be revived by electrodes that shock your heart back into life; but that's unlikely to happen if you've got a shit-load of fentanyl still in your system).
Dachshund - the WONDER HOUND
DLM....Dachshund Lives Matter !!