Steam Deck verification includes things like text being legible and buttons showing up correctly in prompts and mapping, etc. For example, Civilization VI has a Linux native version but is not verified because some game text is too small, and it might require some typing using the virtual keyboard which may not pop up automatically when required.
Totally optional features that come set up by default are not really optional unless they’re opt-in from the start. Most users are not savvy enough to figure out how to disable that kind of stuff.