What is the best resource to learn design for indie hacker?

I believe that most of the design courses etc are shit.

The best way to learn imo is by:

• Copying designs that you already like and remake them from scratch on your own.
• Then take those designs that you copied and do a version of them that will suit your own brand.
• After that you could try doing something on your own from scratch.
• If you need inspiration look at all the design/portfolio sites, dribble, behance, etc.
• Scroll the Figma community to duplicate other designs and learn from them. Insert certain elements into your own designs and build upon them.

Look up youtube videos or guides only if you get stuck with some part.

It's just like being a developer. Usually the really good developers build stuff that they want/need and figure things out on the way, the worse ones come from reading books or taking 10week bootcamps.

Don't focus on reading or learning, focus on designing ;)

I'd recommend - Learn Design by Figma

Really great way to learn to design.

https://www.refactoringui.com/ has some great tips on UI design

https://www.invisionapp.com/inside-design/guide-to-design-systems/ Can serve as an entry point to learning more about the overall ecosystem

While not directly web design, some companies have guidelines that are helpful to think about. Example: https://developer.apple.com/design/human-interface-guidelines/