In 3.36, we will use a heavily blurred wallpaper on the lock screen.

As that wallpaper will be unrecognizable, there is no good reason to
pick a different one from the regular session. The shell will therefore
stop using the separate lock-screen settings.
The popover isn't needed anymore because it would only have one option:
to set the wallpaper. And an additional option for the recent section to
remove the wallpaper for the list, which can be done via a overlay
button.

GNOME/gnome-control-center#864