Not saying it is easy, just easier than you think
I am converting a ZX Spectrum keyboard into a USB keyboard using a Raspberry Pi Pico. It's been a lot easier than I remember these kinds of projects being in the past.
The Pico is the Raspberry Pi Foundations microcontroller board based on their really nice RP2040 microcontroller chip. There are even kits containing everything you need, just add code. Here's my macro pad for live streams that I built back when I worked for WP Engine and ran an online conference.
I'd like to draw your attention to my expertly designed ui.
In the past we would need to use a board like the Arduino Leonardo/32u4 and C/Assembly code, but now we can use off the shelf Python libraries. You might think we need better performance, but micro python/circuitpython operate plenty fast enough, especially when converting retro computers like I am.
Really, though, keyboards are not at all complicated. Once you learn how to read digital inputs such as momentary switches, you pretty much have what you need.
Things only get more complicated due to having fewer inputs than keys you want to read, and outputting the correct codes in the right timing so capital A comes out when both SHIFT and A are pressed together. In the field these are often called "Chords" like in music.
Of course you do not need to custom code either, look into KMK which is really easy to get started with.
Add to this the wonderful selection of key switches and keycaps, there is really no reason now to be stuck with a keyboard that doesn't suit you 100% perfectly.
It's not something I've looked into, but I know some people obsess over keyboards. Do the old computers use the same controllers for their keyboards? I vaguely remember doing stuff on the Beeb to read when more than one key was pressed. Since then I've used the old DIN plug keyboards and PS/2 before it all went USB.
3D printers open more options if you can print your own keys. I need to look into Tinkercad as someone at work recommended it.
!BEER
Old keyboards don't use modern switches but always work on similar principles, at the end of the day it is just making or breaking a connection.
Tinkercad is lovely if you just want to bash something out, I use Onshape for more complex stuff usually. Main think tinker is missing is things like chamfers/bevels and a proper history (it just has undo), they even added sketches recently
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BEER.What a fun project. I have an old IBM M keyboard that I was using for a while. That thing is so awesome. I wish they still made them. I know there are alternatives and refurbished ones, but there is just something special about the M.
Jealous! Those are like the Rolls Royce of keyboards
:) I've gotten a lot of use out of it. I just wish it had a USB connection. The five pin DIN connectors aren't easy to come by anymore on motherboards! :)