Windows 11 shell UI seems to be mostly web. I remember how during beta testing people kept finding widgets were you could accidentally trigger Chrome's caret browsing prompt when pressing F7.
Even Microsoft's native applications can feel off. For example, I use Outlook for my email and really dislike its editor. When I type, I want the text to snap into existence immediately as I type. In Outlook it feels like it glides into being and doesn't even keep up to fast typing. Word is like this too, but fortunately I don't have to use it very often.
Because of this, I write longer emails in a text editor and paste it into Outlook when I'm done.
Every month or after a fresh install you can't start the clock or calculator app because it needs an update. It's not even an automatic update you need to open the app to get notified that there is an update. Insane.
Which parts exactly? If anything explorer.exe has never been more native (it used to have a lot of HTML elements in Win98 to XP). I think new control panel and start menu are WinUI based.