There are actually three modes for your typical FPV quad. I copied this from a website and it explains the differences.
What DJI calls ATTI mode is basically Angle Mode.
Angle Mode
The stick controls the angle of the drone, and when the control stick is in its maximum position, the drone will hold the maximum angle of tilt allowed. When the stick is released, the drone will become level with the ground. It does not allow the drone to flip.
Horizon Mode
Horizon mode, unlike Angle, allows the pilot to perform flips and rolls when the stick is in its maximum position. However, it is worth noting that flips in Horizon mode are not fully acrobatic, and the Acro mode is better suited for aerial stunts.
Acro Mode
It is also known as ‘Rate’ and ‘Manual’ mode, depending on the manufacturer. The drones are not self-adjusting and will continue on the same course and angle that was last provided by the pilot when they take their hands off the sticks. The acro mode gives complete control of the drone to the pilot and is thus not entirely suitable for beginners. If the stick is placed at an angle, the drone will continue to rotate along that angle and will not maintain a straight course, and when the pilot lets go of the stick, it will not level itself, and the pilot must use the opposite controls to level it themselves. It is a difficult configuration to learn, but is fully acrobatic and the pilot is not limited by the controls.