Why is it that when taking a photo of a person, the object next to it is empty and when taking a group photo, it is aimed at one person and others are empty?

I think what you mean is that using the same camera is similar in operation and setting, but there are different background blur effects when shooting a single person and taking a group photo.

Just for your reference, there may be the following reasons (because I don't know your camera model):

1 Shooting distance. Generally, when taking a single photo, the camera is definitely closer to the person being photographed than when taking a group photo. The closer the camera distance, the shallower the depth of field.

2 focal length factor. When taking a single photo, you may use a longer focal length (to make the image bigger), while when taking a group photo, you usually use a shorter focal length to "widen" your field of vision. The longer the focal length, the shallower the depth of field.

3 shooting mode factors. When taking a single photo, it is possible to use portrait mode, in which the camera will use a

larger aperture. The larger the aperture, the shallower the depth of field.

4 As Flying Swordsman said, the background of a single photo may be farther away from the figure and the focus, which is easy to appear blurred due to the shallow depth of field caused by the above factors; The distance between the people in the group photo is relatively consistent, and of course it will not be affected.