Windows 10 Dark Theme only applies to Metro Apps, such as Settings, Alarms and Clock, etc. As you obviously know, it doesn't apply to non-Metro software - i.e. the 95%. Dark themes in File Explorer, Office, Bowpad, etc are baked into the application themselves.
Calibre uses the Qt software to provide the UI elements across three desktop platforms - Windows, MacOS, and Linux. Qt does not support themeing under Windows. Other Qt based software products are in the same boat - Sigil, qBbittorrent, falkon, malwarebytes etc.
I don't know if The Qt Company has anything in the pipeline in this regard. But I imagine they've been asked about it a qtrillion times.
BR
|