What I've seen, individual cops and police agencies are rarely anyone's political arm. The district attorneys in charge of prosecution, however, are another matter. 2020 was full of stories out of places like Seattle and Portland, where cops would arrest and bring in people, DAs refused to prosecute, folks got sprung in time for the next riot.
And of course, the decriminalize-stuff movement had a bunch of legislators making things like vandalism and theft not-arrestable offenses. Colorado Springs cops flat out told me they usually don't arrest for simple assaults, unless there are other factors at play. Basically, you can walk up behind someone, deck 'em hard, hang around to get your ticket and summons, then go back to your lunch. Sometimes this can be due to jail capacity too.
But yeah, the notion that Mirkwood and team only beats up on maga-hat wearing folks, and turns a blind eye to black bloc wearing flash theft mobs, yeah, doesn't really work that way.
Now, when there's protesters and counter-protesters that start fighting, sometimes cops will see things on the ground, and one side ends up getting cuffed. No matter who started it/was more dangerous/engaged in criminal activity, the media and video from the scene will usually be edited and spun to portray one side's narrative. One person's "Rich white guy runs over black student peacefully protesting", is another person's "the elderly driver was surrounded when stopped at a red light, and accelerated to save his own life after they started busting his windows to get at him".
Tomorrow marks the 2 year anniversary of this stuff visiting Provo, UT. The video is still up: https://universe.byu.edu/2020/06/30/two-sides-collide-leading-to-march-down-university-ave/ Does anyone else remember all the many ways that thing was portrayed?