It’s completely illegal but the people who do it are conservative white men, so the police almost universally look the other way (it’s extremely common to see the trucks equipped with this also have blue lives matter or fraternal order of police stickers, those thin blue line flags the fascists like, etc.). You can see them intentionally blast cyclists, pedestrians, Prius drivers, etc. so it really should be treated as assault since there’s both premeditation and deliberate targeting.
What really needs to happen is nailing the shops which do these modifications. Individual drivers are hard to track down but if it involved your business going bankrupt they’d decide it’s not worth it very quickly.