Nah they def use Instagram, but more as a landing page, Its not cool to post a lot, people in their 20s will have their old posts,rarely posting new ones, but with updated stories.. Teens will have 1 or ZERO actual posts(much cooler), and sparingly use stories, and the stories collections/archive on display above posts are the 'new' way to post. Hardly know any teen or 20 something that uses snapchat as tiktok replaced it years and years ago