[Feature]: Add system theme synchronisation option

[ReadOnlyMAIN]

Description

This is just an enhancement, but it would be nice if there was a third option in Appearance>Display>Theme named "System" that automatically changes the application theme (between Light and Dark) depending on the system preferences.

Additional Information

This could also be the default setting.

[DavidLazarescu]

Thanks for the proposal. This is planned for windows, but doing this on linux with Qt is not possible afaik.