1. UI design
2. UX design
3. Landing Page design
I own all 3 and they are among the best purchases I've ever made, even at the cost. Erik is a former programmer who has taken the engineers mindset and systematically analyzed and broken down the various parts of UI design. It is very practical, which was something that was lacking in most resources I found when I was in your position.
If anyone is interested, I would recommend starting with the UI course, which probably runs around $1000. Unfortunately It is only available at certain intervals, probably every 6-8 weeks.
If the cost is intimidating, you can get a lot out of his blog, which will also give you a taste of how he thinks about design: https://www.learnui.design/blog/.