The core computing needs of the vast majority of people has not changed in the past 10-15 years or so (perhaps even more). Text processing, image/video editing, web browsing, spreadsheets, presentations, etc are all fundamentally the same. Sure, videos are now 4K instead of VGA, and webpages now weigh tens of megabytes instead of kilobytes; but the fundamental, underlying modes of creating and editing are the same. The worst part is that the experience was often better a decade or two ago! This is why you have professionals like GRR Martin using WordStar to do their deep work.
Even for programmers, the fact that many are still living in vim/emacs shows how little the core operations of computing have changed.
I would love an OS that focuses on offering stable, well integrated, well designed functionality and interfaces, and does not change every 12 months because the marketing/design people were bored. Releases would instead focus on stability, performance, and bug fixes. Adding support for new data formats as they appear would be required, but not in a way that needs to change anything on the end user side of things (your photo editor can now open/export HEIC, great!).
I know that most of my family would be happy with something like this, because I hear them complain all the time about how some software update changed where everything was, or even worse - removes functionality they needed.
In a weird way, I think the closest thing to this that exists today is Mathematica - reading interviews with Stephen Wolfram about how he uses it is fascinating. I’d want that, but for everyday users, not geeky mathematicians :)