Blast from the past: Z80 and 6502
The old computers are much simpler and much easier to understand than the modern monsters, so getting into the retro scene has immense educational value.
If you want to get into the retro scene, I suggest you check out Z80 and 6502. There are extremely vibrant communities around them. The 6502 is still manufactured, while the Z80 was discontinued recently (2024).
Because of the capabilities of the technology then, the size of the transistors, and complexity of the machines and the production lines that make chips, they had to make a lot of tradeoffs in order to make the products viable. The instruction set architecture is very complicated and has quite a lot of quirks. Despite that, it is a great learning exercise to make something with them.
There are many kits and books you can buy to build your own computer with them, and of course there is Ben Eater's series on how to build a 6502 from scratch.
MicroBeast (https://feertech.com/microbeast/) is a particularly cool one.
