brilliant.org is the site of that sort that's always mentioned at the end of a bunch of engineering channels. I tried it and it wasn't really my thing, but it sounds like just what you're looking for.* I just didn't like it because it's TOO interactive (requiring click after click after click, with many simple questions in between), but it's good for learning something you know nothing about.
* Here are some referral codes for Brilliant if you want to sign up (no affiliation to me). They all do the same thing, give you a 20% discount and help sponsor a engineering or science YouTuber (of your choice):