In mode ADV there is a menu where background is blurry and face is clear. It works perfectly when taking 3 or 4 pictures. Does anybody knows how it works.
I believe the camera focuses where it normally would (e.g. center focus) then captures additional images, one or two focused closer, and maybe another focused further away. Then the images are combined in-camera.
The closer-focused image shows better background blur to combine with an in-focus subject at medium distance.
Documentation says "up to 3 shots" so I don't know where you got "3 or 4" shots.