Domestic political groups are covered by constitutional protections, freedom of speech, association, assembly etc. no one gets rounded up for their beliefs or membership in a domestic political group. What is being done are investigations to identify individuals who committed crimes like arson, assault etc. extremists on both sides are aware of this, hence the face coverings, having everyone dress in black or dress alike etc to make identification from photos and video more difficult.
Regardless, most of the mass violence we have seen was perpetrated by straight up opportunistic thugs /hood rats coming out because bored/corona/ Fuck The Police.
In my area we saw only a small core of Antifa adherents 10-15%, often acting as agitators for the hood rats. In more liberal areas like Seattle, DC, Austin etc you will see that percentage go up due to the local population and drawing extremists from other areas but it won’t be much over 25%.
The organic nature of modern social and political movements in the era of social media and secure communications apps is something we are just beginning to grasp. As with many paradigm shifts, the young, raised in the new reality have the best grasp.