I mean start from scratch as much as possible and rethink how a computer is used by most people.
By all means keep Windows around for enterprise but build a new OS that is forward looking and eschews backwards compatibility when virtualisation can be used instead.
Aggressively simplify the OS. Make it consistent with a UX that keeps the OS out of the users way. Contain software from vomiting itself across your system. Make things discoverable and consistent, don’t impose restrictions such as locking open files.
I’m coming from this as a user not an OS developer. I use a mix of MacOS, Linux and Windows from day to day. Windows is often a dinosaur and constantly gets in the way. Each new version of Windows is another layer of paint over an existing peeling layer. Certainly Windows can be performant and it would be foolish to throw it all out.
I understand a lot of this is hot air, and your question is asking about specifics. I’m coming from this based on my observations on how students and elderly relatives use their computers.
I’ve moved my parents to iPads. They’re simple and they can do whatever they want to get done. They can browse the web, watch video, FaceTime and see photos of their grandkids etc. At the worst I have to run an OS update for them. They always forget the passwords but TouchID takes care of that.
Meanwhile my father in law has his ongoing war on technology with lists of passwords, frequent manual backups, and lists of things that need to be fixed whenever we visit. The computer is a ticking time bomb to be feared.
My students frequently have no idea what a file system is. Files are scattered everywhere on disk and the cloud. They have no idea what a USB drive does and some think simply just plugging one in magically copies the relevant files somewhere.
Usually by the time I’ve finished with them they’re writing code or running WSL or playing with a raspberry pi or whatever.
So we have this gap. There is the older generation where computers are scary and they’re happy with simplified but robust devices. There is the younger generation where most of them live on their phone and have no clue how computers actually work. When they end up in a job they’ll plod along with excel and whatever enterprise software they need. It really doesn’t matter what version of Windows or Office.
In the middle there are some people (of all ages) who actually have some degree of knowledge.
My solution is to make the desktop OS easier to use while still providing the complexity that is required as one gains experience. Right now Windows is intimidating and outdated.