I've been doing this for well over 20 years now and I taught myself by building Geocities sites and random stuff.
Just build things and push them to a repo. Have an idea for something? build it. could just be something like a TUI for Mastodon or like an eReader with AI driven text to speech, I don't know i'm just spit balling here but my point is you just have to build stuff. It's like anything, the more you do it, the better you get at it. Like drawing. you just draw something every day and eventually you get good. it's the same for coding. just work on something every day and you'll get good at it.
So just build something or contribute to your favourite open source project.