The problem with Navigator/Inspector panes introduced in Xcode 12 is now fixed. As I'm sure you know, in Xcode 12 the state and position of panes wasn't saved with a particular tab, like in earlier versions, but changed globally instead. In Xcode 13 the normal behavior is restored.
For example, I can have the Navigator pane hidden in my xib tab (as I never need it there), while having Navigator shown in other tabs etc. Yay. Can now work normally like before.
Also, the project name with icon is now restored in the toolbar.
Not so good:
I'm not impressed with the new file and framework icons, but it's a minor thing.
The big problem is that they removed color from the folder icons and they are now grayscale.
WHY? Not a single user ever asked to make folder icons less visible and more boring, as well as uglier. In BigSur, Apple finally did something right at and restored colors in sidebar icons almost everywhere. And yet Xcode team now does exactly the opposite.