What does the autopsy report say he died of?
According to Dr. Michel Badin, Floyd died of Mechanical Asphyxia. The Chinese flu was a contributing factor causing Floyd's lungs to deliver insufficient oxygen to his blood. What oxygen that was being delivered to his blood from his lungs was being further compromised as it flowed into his brain. This came with Officer Chauvin's knee compressing his right carodid artery. That compression was what Dr. Baden called Mechanical Asphyxiation. This was further compromised when Officer Kueng was holding him down, compressing his lungs from free breathing. Then, you have to consider the condition of Floyd's heart. After years of drug addiction, his heart was not healthy. Floyd had high blood pressure. The Meth that Floyd was taking, caused his heart to race and his blood pressure to go higher, even when it was not getting enough oxygen. A heart racing on Meth is not what you want a heart to do when it is being deprived of oxygen.
The brain, due to lower oxygen levels caused by Officers Kueng and Chauvin, was signalling the lungs to lower respiration as well as the action of fentyanal which also lowers respiration. With compromised lungs, due to the virus, you do not want lower respiration levels to deliver low oxygen to the brain stem (where respiration is controlled). The result is the stopping of breathing. With the heart racing from meth, you don't want to stop breathing. The heart stopped because of lack of oxygen when the lungs failed.