Earlier quoted context omitted.
Step 1: for some reason, the world stops making computers, but keeps the ones that already exist Step 2: 100 years pass Step 3: computers are now an old (and dying) tradition, kept going only by a small group of people who understand how to care for the machines. Was that so hard?
Step 1 is really hard if computers are useful (why do you stop making something that's useful?), but step 3 is simply not believable: a society that has machines that could, at the minimum, help solving complex calculations and engineering problems much better than humans decides to completely ignore them. That's not how societies work.
Sometimes someone manages to spin up new manufacturing of retro components or things to replace the retro components (there are a few pcbs running around that can replace floppy drives that conform to certain interfaces with usb sticks or sd cards or even a network): Vacuum tubes, parts for vintage cars, parts for vintage watches, vinyl records, etc. but often before that happens the entire known supply needs to be scavenged.
So I can imagine a world where we manage to start doing the things we are doing with some new technology that is not digital silicon based computers that run on electricity. But there will be edges where the new technology is not compatible with some system, and in that edge lives this kind of speculation.