Training is not the problem IMHO - there is no training on the planet that would have altered the interactions between Chauvin and Floyd.
Covering for the bad apples, insane laws that protect cops who abuse their power and the seeming need for 'being the one in charge' and demanding respect are the problem. In short asshole cops need to be fired. You can never get them all but there is an overabundance of cops that think they can abuse the shit out of people because they get away with it. I have had encounters with both types and the bad apples are far to damn common. I have had my person robbed ONE time in my life and it was by a cop. He thought it was just fine because I 'didn't belong' where I was.