So, this isn’t exactly retrocomputing and it looks like it’s from four years ago, but I just found it and thought that many here may find it interesting.
This guy built a simple 8-bit CPU out of essentially discrete logic circuits (from what I’ve see so far, nothing more complex than a 4-bit adder chip) and explained the entire process.
Silicon foundries use a lot of water and raw materials and contaminate the ground. Full degrowth may involve abandoning semiconductor technologies and making computers out of simpler parts, such as electromagnetic relays. They’ll be a lot slower and simpler, but with the right knowledge, one can make them from raw materials without bootstrapping a complex technology chain.