The CPU is far from being the most sophisticated component of a computer.
At least if we're talking about #permacomputing, or, rather, scavenging and collapse computing. Okay, maybe in open source hardware, too.
Designs of new hobbyist computer architectures are seemingly revolving around inventing a CPU and/or mapping the peripherals on the system bus.
And you could find many simple CPUs based on FPGAs, logic chips, transistors, valves and even relays.
What you usually don't find is custom RAM. Before Intel introduced cheap solid-state RAM in 1969, there were at least six contemporary competing types of RAM used in computers, and at least as many were already considered obsolete.
What you don't find is peripherals. There are rare cool appliances, like punch tape readers. But have you seen a custom hard drive? A printer?
All these are "easy" in terms of relative complexity for industry. But they are simultaneously very hard for a hobbyist/DIYer/tech collapsnik.
@nina_kali_nina I've built a printer from scratch, but it's an electromechanical contraption not directly related to computery things and not exactly a convenient form-factor.
(though watch this space, I still have loads of ink and I've been Having Bad Ideas for future projects after watching too many teleprinter videos... 😳)