What is the intended purpose of the leveling bubble when camarea grid lines are enabled - particularly as the bubble is only activated when the camera is held in the horizontal plane?
Another site explains for the S20, "Either camera (rear or front) can be enabled to use this feature, but you do have to be in photo mode. The intended purpose here is to line up landscape shots, but because it's using the phone's internal sensors to line up those two dots, it works as a highly accurate level, too!"
The grid lines help in taking a 'level' landscape photo, but the bubble only activates when the phone is held in the horizontal plane, i.e. held flat like it might be when left flat on a tabletop, not when held the in the vertical plane when taking a photo.
This link explains what I mean...