Portland Police Department is just one particularly egregious example. Numerous leaked text messages between officers and the Proud Boys. Letting them know to take cover before tear gas is deployed and that they'll be told when it's "all clear" to come back out, letting them know that though some of their leaders have active warrants for arrest, that they are clear to come to the protest because there's no "other agencies" involved in enforcement, so there's no risk.
People who Molotov cocktailed a police van with people inside. Let off with probation.
Police beat an unconscious person until they died. Internal investigation cleared them of wrongdoing.
It definitely matters what the protest is supporting/fighting.