Refer to documentation of page sections:
In the Interface theme selection, you can switch to Dark theme. On Windows 10, the default Automatic mode switches the theme according to “Default app mode” option in Settings > Personalization > Colors. On older versions of Windows, the default Automatic mode always falls back to the Light theme. For the best dark theme support, Windows 10 May 2019 Update (version 1903) and latest beta version of WinSCP are required.
Check Commander to select Commander interface.
Check Explorer to select Explorer interface.
Before your selection, you may first learn more about the WinSCP user interfaces.