it depends on the crowd, take for example (iirc) one of the embers from the last war modules was an artificer lab kind of thing with a staff breakroom (or I added one when I ran it)... blending in there would probably be arcana or some relevant tradeskill type tool profession to pass oneself off as part of the usual nerdytype staff or at least someone who belongs in the building... blending into the crowd at a high society event might be knowledge nobility... but that doesn't exist in 5e & was poorly scoped iwhen it did so goes back to diplomacy for everything, but I might also allow creative application of chef-tools(cha) or something because those types of jobs require some level of understanding how to interact at that sort of event. a generic crowd like busy Manhattan streets/parade spectator crowds/etc would depend on if it was planned surveillance(when was the last time you asked a guy with a telecom shirt, hardhat, clipboard, & some specialized looking tool for proof of his job?), attempting to escape (intimidate no questions!), or escape streetwise(wis) or similar to know how to turn into the right kind of a store/alley/etc & vanish probably but there is -no- skill that even kinda applies for this in 5e.What roll would you call for when trying to blend in to a crowd? I don't see that Dexterity has anything to do with it, personally.
You could add a bunch of skills to fix a lot of these things, but that leads to problems because you either need two pools of skills or you have to make a lot of changes to a bunch of existing overly inclusive too widely scoped skills