Do you have links for learning C that you think are good?

Well, the way I learned C was by taking this class many years ago: https://see.stanford.edu/Course/CS107 (not this specific instance of the class, but same instructor so I assume the curriculum is the same...).

There are surely more efficient ways...

What would you consider the more efficient ways to be?

I'm sure there are good books... what are your goals and where are you starting from?

C syntax is very simple and there aren't a huge number of concepts you need to learn (memory layout, pointers, the preprocessor, casting).

There are tons of projects written in easily-understandable C. cpython is one.

I already know higher level languages like Python, Java, and a handful of others, but never really dove into C much beside the Kernighan Ritchie book years ago. I was able to do some stuff with an arduino with it, but my goal was actually always kernel development, or maybe rockets at SpaceX.

If you want to get into kernel development (something I have no experience with except reading headers for various userspace interfaces), perhaps starting with an education OS is good. I did take OS in undergrad and that was probably where I got most familiar with C.

This might be a useful place to start: https://web.stanford.edu/class/cs140/projects/pintos/pintos....