>I have realized that I love building software, and I suck at marketing.

-> it's not marketing you suck at, it's building for someone else that you do

>However, as a techy, I can't seem to build useful things, or things that generate money.

-> build something for someone else, don't think about revenue. Even if you build for 1 person, something will click when you see they're using what you build and only then you will figure it out.

Think of it like this:

-> do you have someone close that calls you when they have a problem where you're the expert in(something computer i'm guessing) - if yes, do the same thing, but build something after you understood their pain, iterate until they cannot live without your solution(big/small whatever it is) - don't let them design their solution - you're the solution designer, you need to understand their pain.

This is the most practical comment I've seen on this.

That's exactly what I experienced too.

Building for others is scary at first, because you can (and definitely will) face rejection sometimes.