Imagesource: Jan Rösner

Nand2Tetris should be familiar to pretty much anyone who has studied digital design and processor architecture independently of a CS degree. The course basically tells the story arc from how a transistor works, over digital logic, to fully functional processors, compiler construction, and programming in a thoughtful and very focused way. Super interesting, but also tedious.

Alternatively, grab Ben Eater's 8-bit computer videos, and rebuild them in a circuit simulator like Digital or Logisim. But if you don't like the whole bootstrapping behind it, the following might be a good place to go:

The NANDGame by Olav Junker Kjær. Basically a cross between Logisim, Nand2Tetris and an online course in the browser.

May sound boring to some, but it is quite the opposite. Especially if you want to refresh something, you have learned years ago. The project is not brand new, but unfortunately only touched down on our desktops this week. Definitely worth a try, because high-quality learning material with participatory character in the segment is unfortunately far too rare.