There’s wikiversity - https://en.wikiversity.org on all of different topics.

And several others are trying to create mind maps.

But would be great to have a resource like OSSCSU or TeachYourSelfCS for X...

At least for the “main” subjects like Maths, Stats, Chem, Bio, Physics and Humanities - Econ, Anthro, Pschy, Pol Sci, Law, Sociology.