I’d rather to see the settings in the same windows (Avast interface).
But this could not be an unanimity and some users would prefer a second window (resizable).
My suggestion is on the middle: a docked window that:
- Will open inside of the interface, using all left space (picture 1).
- Users can “separate” the settings into another window (resizable), like it is right now.
- Clicking in other menu entry will just get the user to close settings and go to the other page.