I think a great piece of advice for people who want to learn, but don’t know what to learn, is to take advantage of Wikipedia.
However, the second half of this advice is use that specific feature where some words are highlighted, and fall into rabbit holes. The best part about this is you don’t have to have anything super specific to search.
Say, for example, I was in the mood for some ELA type stuff, but I don’t know what kinds of stuff there is. I simply go on Wikipedia and search English. Admittedly, that doesn’t bring up much, but there IS a blue link to a page about the English language.
From there, I can click on things like “Indo-European language family” and “early Medieval England” and “British Empire” if I’m in the mood for more history things. Or, if I really want to learn about words, I can click the vocabulary section, or the phonology section, or the orthography section, or even the grammar section.
There’s so much to be learned in this one broad category, and it’s the same for every other subject you learn in school, which is a great place to start.
Math (mathematics)? Empirical sciences, number theory, and set theory are just in the opening paragraph. Not to mention the sections titled “relationship with astrology and esotericism” and “symbolical notation.”
History? Well, from history we can get to History of Earth, and it’s not hard to guess how much is there. There’s also anything that could be the History of; History of Mankind, History of Dinosaurs, History of Philosophy, literally pretty much anything you could want to learn about is on Wikipedia.
The point is, Wikipedia is an amazing tool and source of knowledge. This strategy is a great way to actually access that knowledge. Have fun!