If they could arrest people for what they've been doing, they would have already arrested people. And they have arrested a few here and there for "assault" (things like daring to react when being shoved by an annoyed officer), but the thing that's really pissing DHS off is that the protesters and observers are not breaking the law.
one person walking away from a police encounter doesn't mean police think that person did not break the law.
prosecutors may take their time and file charges at their leisure.
Remember that most of the participants in J6 walked away and were later rounded up and arrested across the country once the FBI had collected voluminous digital and surveillance evidence to support prosecution.