In my opinion most topped shots are caused by the lead arm breaking down at the elbow and or wrist. The lead arm is the radius of the swing arc and when that radius shortens, the club head will belly the ball. The lead arm typically shortens when the players body stops rotating or the player tries to hit up on the ball with a scooping action.
Either way the best fix is to “rotate and reach” meaning visualizing just past impact with straight arms and the belt buckle to the target.