Comment by fibonacci112358

I'm not 100% sure, but I think the main reason the new Win11 apps like Notepad, File Explorer, Task Manager have a slow UI and the piece-by-piece drawing issues is because they combine UWP (the "new" tech) with the old Win32 controls, they are not a from-scratch rewrite. There seems to be some big overhead in using the two different UI frameworks together.

There was an attempt to make a Chrome OS competitor that had the entire UI rewritten in UWP, and when that got canceled it seems MS saved the new start menu + taskbar and bolted it on top of Win10, and for Explorer and other apps made this UWP+Win32 abomination. Actually when you profile Explorer you can also see DirectUI running, which is I believe another UI framework from the Office org. this time (maybe it's related to OneDrive).

Btw, apps written in C# using WPF can be surprisingly fast, so it's not really a problem of .NET managed vs. native apps. For ex. may favorite Git GUI (git-fork.com) is C#/WPF.