From Greer's point of view, the factors that make today's hardware brittle are not technical, but economic. Corporations have to make electronics at a profit, and at a price point that is accesible to the average working class citizen. This business model would not be sustainable in the either a fast-collapse or slow-collapse scenario.
Instead, in the novel, governments take over the tech industry sometime in the second half of the 21st century, and treat it as a strategic resource in its struggle to not be left out in the global musical chairs game of climate change + resource depletion. They run it at a loss, and put the best minds they can spare to the task of making a computing infrastructure that is built to last.
By the 25th century, which is the time when the novel's events take place, Humanity has lost the ability to manufacture electronics, but computers built 350 years ago are kept in working order by a cadre of highly trained specialists (most of which have the skills of a geeksquad employee, but still). Common people have maybe heard some wildly innacurate legend about robots or computers. Wealty individuals are probably better informed but still cannot own one of those at any price. They only computers depicted of spoken about are US government property operated at US millitary facilities (or maybe there was one at the Library of Congress, do not really recall, though).
There's one post-collapse hacker in the novel, a secondary character that is part of the protagonist's crew. The author is not an engineering type and dances around the actual skills of this guy, but I'd say he seems able to use a debugger/hex editor and read binaries. His greatest achievement, though, is to fix and set up an ancient printer and recover documents from a disk that was "erased" but not wiped clean.