[DiapDealer]

Sigil uses Windows' light/dark theme. Change Windows to dark/light and Sigil will change with it. The preference setting you're talking about only affects Preview when in dark mode.

For the record, Sigil has had a dark mode on Windows for a long time. If Windows used a dark theme, so did Sigil. The change with Sigil 2.2.0 is that "live" switching is possible. No need to restart Sigil when the Windows theme changes.