How to learn UI design as a Developer？

Look into the practice of "copy work" to master what the best designers do, eventually, you'll develop the eye to create excellent UI. Join UI design challenges like 70Rad, or even copy the best product screens from Mobbin (Airbnb, Headspace, etc), do the same if you want to design websites using Awwwards, and see your design skills grow exponentially. This is what helped me upskill when more than years of education, theory and real-world projects didn't help. Look for this video on YT for reference: The EASIEST way to get better at UI design in Figma

First of all, great step thinking that as a good developer you need to understand design. Taking courses and all is great if you want to deeply understand design. But if you want to learn design so that your development skills become smooth, I'd say, get your hands dirty by exploring design systems. As a developer, you will always have a design to build upon. But to be able to build pixel-perfect, you need to understand how the design is done. A good design is built on a good design system. That's my suggestion.

The best way for me is through online courses: there are many online platforms that offer UI/UX design courses, such as Coursera, Udemy, and LinkedIn Learning. these platforms offer comprehensive courses from beginner to advanced.