Since commit 3c6eae3 it is not possible anymore to set a custom titlebar color via "TitleBar" in a theme.json. It is hardcoded to the transparent mica style when using Windows 11. This looks especially bad when using one of the dark theme overrides.

It is fine to use mica by default, but it should be possible to control the behavior from a custom theme as before. Optimally the theme override should also allow to set the SystemAccentColor for the titlebar.

And a minor nitpick:
The close button hover color should have the windows default hex code #c42b1c with a white x instead of maximum red #ff0000 ;)