Prior to the new law, California police officers could use deadly force if their actions were considered “reasonable.”

…The new standard restricts lethal force to when it is “necessary in defense of human life” as perceived by a “reasonable” officer and based on the “totality of circumstances.” It also emphasizes deescalation as an effective alternative to lethal force.

If questioned, officers will have to prove there is an “imminent threat of death or serious bodily injury,” and they’ll be evaluated based on the facts they knew leading up to the deadly action.

To get the bill through the Legislature, Weber accepted amendments that eliminated provisions that would have made it easier to prosecute officers. [emphasis: peanut gallery]

…Some of the bill’s original backers, including Black Lives Matter, withdrew their support after the legislation was “so significantly amended.”

What’s does CA use of force law mean for cops, minorities? | The Sacramento Bee

So basically this was just an exercise in PR and nothing has changed. Cops who kills will not be prosecuted for the violent crimes they commit.