I don’t know much about electronics, but I’ve learned almost everything I know about cars from YouTube and forums, and now I’m a pretty decent at-home mechanic. You pick up a lot of basic knowledge and theory just from watching/reading about others diagnosing and fixing their issues online

YouTube is your friend; like you mentioned in your post you can learn how to do almost any project on there. Forums are another great resource. You could always pick up repair manuals or maybe even electrical engineering textbooks if you want more.