Wordpress is huge, but plugin development isn’t too hard once you start practicing. Things do change, so staying flexible is key. I’d recommend starting with this book: https://johnparankimalil.com/wp-content/uploads/files/wordpress-plugin-development-sample-chapter-2-social-bookmarking_0.pdf
If you want to see how simple plugins are built, check out mine. They’re well-documented and split into complete packs and individual components, so you can easily see how everything works.
You can find them on the official plugin repository:
I build plugins too! If anyone needs help, feel free to reach out. Here’s a link to some of the plugins I’ve built. They’re free to download!