Hello,
Sorry to hear you are having issues. I believe the area you're referring is by design by the skin author. It was added skin area which is there for the new Windows 11 tabs features. If you try older Luna theme you will get the full blue titlebar but the Win 11 explorer tabs will look out of place. Refer screenshot below.
If you do not wish to change the WB skin, while you on Windows dark mode, please disable this option.
Thank you,
Basj,
Stardock Community Assistant.
