I disagree, I don't think Flask is better for learning than Django,
It is true that many components are already built inside django but the complexity is not really hidden, the developers still need to understand how the framework works.
For sure you can create a basic view with a ModelSerializer by hiding all the complexity, but very often it won't be enough to build what you want to build, and therefore you will have to search trough the documentation how things works.
In my opinion both Flask and Django are good for learning purposes, but Flask requires the user to handle more complexity than Django, which is not always the best thing if you want to learn
It definitely boils down to personal preference in the end. I always hated trying to wrap my head around solutions before understanding the problem.
By using Flask first, you also end up thinking "wow, every time I build a flask app I go through these same repetitive steps. Would be nice if they were automated". Then you find they are automated in Django.
If you learn the solution first, it seems irritating and sometimes you never understand the problem that it's solving.
I think one of the big reasons to try Flask first is to learn what magic is under the hood. If you start with Django, you're asked to build your MTV in a very specific way. That way Django can give you stuff like XSS/CSRF protection.
If you don't know what magic Django is doing for you, it feels restrictive to do stuff the Django way.
For sure you can create a basic view with a ModelSerializer by hiding all the complexity, but very often it won't be enough to build what you want to build, and therefore you will have to search trough the documentation how things works.
In my opinion both Flask and Django are good for learning purposes, but Flask requires the user to handle more complexity than Django, which is not always the best thing if you want to learn