There is no right or wrong way, the MVC pattern gives you the guidelines for the separation of concerns, it does not tell you how to name or organize things.
Here is how I think the MVC components map to a Flask app:
The M is the easiest to understand, as models are pretty clearly specified. What is sometimes not completely clear is that models are not just the database abstractions, the business logic of the application is also part of the models.
The V covers the presentation logic. In a well designed Flask application this is handled with templates, so I would say that in terms of MVC templates == V.
The C covers a thin layer that updates the M and the V based on input received from the user. In a Flask app these are the request handlers, which have the somewhat misleading name of "view functions". When a view function completes it returns an updated view (rendered template) to the user.