As a libertarian myself, I've come to the conclusion that anything addictive is not really consensual, because addiction can't be controlled. Thus,
selling or providing addictive stuff violates consent of the buyer, and should either be illegal, or have high taxes. Maybe there should be different laws to those who are already addicted and those who are not. Drugs which are not addictive, should be legal, but have all the information about their negative effects on the label.
Imo this should apply to addictive apps as well. The damage here is mostly the time that is wasted.