[ziedaniel1]

To get the key ideas behind many of these topics, you could try reading Evan Chen's Infinitely Large Napkin: http://www.mit.edu/~evanchen/napkin.html

[jacobolus]

Concept: undergraduate with no teaching or writing experience who was an International Math Olympiad gold medalist writes a draft book explaining all of undergraduate mathematics (or rather, most of the topics from his coursework in random-ish order) to slightly younger IMO participants.

It’s great that he’s making the effort, but I’m not sure this is the most useful resource for a typical autodidact.