I think the problem is that what you want to learn is not always fun all the time. At some point you'll hit the wall and you have to overcome it (I admit, however, it never happened to me in programming, but for example I hate driving while I have to get better at it). It's tempting to make an excuse like you're simply "not built for it" - so that you can give up without feeling bad. That is a harm of the fixed mindset as far as I understand. I'm not saying that people should feel bad all the time, but the "nature" excuse is sometimes a slippery slope.

There should be more research in meta-learning. How to learn things that eludes you far too much. Rewire your views deeply. And how to perceive 'progress' while interacting with blind spots.

A pretty good counterpoint to that: Playing an instrument.

Very few people can pick up and play an instrument naturally. The best are the ones that combine a basic musical talent with hours of hard work, in a quest to get to a level where they can "just play".

If you have a fixed mindset, it is probably difficult to have fun with something you want to learn if it just constantly makes you think you are unintelligent.

Are you so confident that this is true for others because you have lots of evidence, or are you just talking about your personal experience?

More precisely, from what I've read the "flow" state seems to be about ideal for both learning and making things fun.

Plus of course, the more fun something is the more practice you'll find yourself getting (and without having to bash your head on the wall).