Introverted people often handle conflict in ways that aren't as conducive to storytelling, without an awful lot of narrative gymnastics. Compared to extroverted ones, anyway.
I don't know that this is true. I can think of viewpoint characters who are what I'd classify as introverted. Introverts have rich inner lives, and if they are the viewpoint character, that can (and should) come out.
But I'm not sure what you mean by narrative gymnastics. What would be some examples?
But I do think this is the case and get exasperated by the stout insistence by a lot of writers that there is NO cultural or societal preference for certain character archetypes, when I'm pretty sure there categorically is.
I think there probably are cultural preferences. It would be surprising if there aren't, but whenever something is an expected norm, opportunities abound to step outside of or deconstruct that norm. There are many readers who want something fresh and different too. Most of the people I've known who write (or even read a lot) are on the introverted side of the distribution.
There are a lot more types of actual people, than there are types of protagonists, because not everyone makes a good protagonist.
This may be true, but transformations (or change) is usually a big part of a character's arc. I'm not saying introvert to extrovert, but an introvert who learns to be more assertive about who they are, or who learns that they can influence people and events without being bold and brassy, could work.
It may be a matter of genre and expected audience too. Literary fiction often focuses more on a character's inner journey, while adventure novels focus more on decisive action and ability to make changes in the world. YA novels often feature shy or withdrawn protagonists, or protagonists who are outsiders in some way. Romance focuses on a dynamic between characters and the emerging relationship's role in overcoming the characters' individual problems. But I can think of romances with main characters who are introverted (sometimes there is an opposites attract thing happening, but sometimes both are introverts, and they find each other). I can even think of fantasy and SF novels where protagonists are what I'd call introverted or shy. I personally don't have much interest in writing stories about "typical" or "sparkly" heroic archetypes, at least not without some twist.
Introverted doesn't mean passive.
I can come up with a list of titles that are examples, given some time and thought. One that comes to mind right now is "Every Heart a Doorway," by Seanan McGuire. The protagonist is far from outgoing or stereotypically heroic (to put it mildly), but she knows what she wants.
Some stories can be about a character finding what they want too, of course.