Support for dark mode feature on Windows

[ndekross]

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Feature description

Could you kindly consider adding support for dark mode on Windows 11? It's currently the only application I use that lacks this feature, making it quite glaring during nighttime usage.

Proposed solution

In the "Settings" tab, under "General Settings," there could be a new dropdown menu labeled "Appearance." Users would have the option to select from three modes: Light, Dark, or System, with System being the default selection. The System setting would allow the app to mirror the overall operating system's theme. Conversely, selecting either Dark or Light would override the system setting.

Alternative solutions you considered

No response

Additional context

No response

[TheOneRing]

Since we plan to use Qt6.5+ with the 6.0 client this should be possible.

[TheOneRing]

Windows theme always picks the light theme: https://www.qt.io/blog/dark-mode-on-windows-11-with-qt-6.5

Win Theme (Win Vista Aero)	Fusion theme:

@michaelstingl should we add a style picker so people can choose?

[michaelstingl]

Fusion theme:

6.0 should switch to Fusion, no config UI needed.

[saw-jan]

Tested on ownCloud 6.0.0.12536-daily20231102 1ed7c6