Without long text, to a good approximation, you just can't convey long, multi-step reasoning chains at the limit of human intellectual capacity.
Personally I've started reading again much more recently, and it's done wonders for what's going on inside my head. I was feeling so dull! I can only recommend it.
It seems very far fetched that an app that looks like HN might become as popular as TikTok, and that's because the TikTok format is excellent at creating something that pulls people in by delivering short term rewards.
I'm not a Luddite, I'm sure there are some creators out there making clever tiktok videos, but that format really isn't conducive to, as you say, "long-term, coherent narrative building and multistep reasoning".
Non-fiction is very good for other reasons and it's good to aim for a healthy mix of the too I think.
Fiction has so much more to offer! On top of what you wrote, fiction helps you to develop an ability to put yourself in others' shoes. Empathy is anyway scarce in this politically-charged and ragebait-filled world.
Fiction has helped me develop empathy and to stay empathetic. It has helped me develop my philosophy of life; morals and values I strive to stay close to. The fictional characters have given me courage during hard times. And so much more.
Lot of people prefer to start with self-help kind of non-fiction which is, IMO, the least helpful category of books. I don't know what draw people to it.
Walk into a library or bookstore. Pick up something that looks interesting (LITERALLY judge a book by its cover for this) and start reading right then and there. If the book doesn't capture your interest immediately, maybe skim a little bit, or just move on to the next book. Also, ask trusted friends that know you well for suggestions.
You have to first know what your own particular tastes are, and afterwards, do the harder steps of understanding why you like what you like, and expanding your horizons. Once you get to the point where you both know what you like and start to know why you like it, discovery just solves itself. Eventually, you'll be able to tune into any random discussion about a book or author, and discern from context whether or not the works in question are for you, even if you don't share the opinions of those you're listening to.
I've also listened to some YouTube channels who review or go through books they've read. Of course it's important to find someone who have similar taste to you or you'll have a bad time.
On the point of "alternate history" I'll throw out "Matt's fantasy Book Reviews" YouTube channel where he also has some alternate history type books he brings up from time to time.
