Insta is like a computer role playing game, where the player usually plays a character that closely resembles themselves, but often as a more idealized version.
When my daughter started playing Hogwarth's legacy, she instantly created a charcter that looked as much as possible like her. Instagram is not that different.
It would be fascinating to take a sample of people, compare their avatars to their real life appearance, and then have them spend an hour talking to a shrink about why they are so similar/different.
Anecdotally, I know many people in both the very similar and very different camps, and a few who are very similar except for some small thing.
When my daughter started playing Hogwarth's legacy, she instantly created a charcter that looked as much as possible like her. Instagram is not that different.