I've been half joking lately that if I wrote an OS, I'd call it Nostalgia OS. I'd aim for a UI reminiscent of windows 98 / windows 2000 / snow leopard. With HID guidelines and a rich, clear, cohesive set of UI widgets to build applications with. I think that was the peak computing user interface - at least as I experienced it.

Of course, the kernel would be based on capabilities (probably SeL4). And applications would probably ship as WASM bundles. And I'd have a built in local first user database built around CRDTs and things instead of a file system, kinda like a modern Lotus Notes. But for the UI? That era was great.