They claim so much and their browsers' code is 100% proprietary so it's impossiblen to verify their lies. This is what triggered the bullshit detector in my head
Far from me to defend Arc (I dislike it for several reasons) but it’s based on Chromium so it’s far from 100% proprietary. Don’t Edge, Vivaldi, and even Chrome have proprietary layers on top of the open-source Chromium?