how can i stop rotating gameobject but slowly

How can i make the plain propeller stop, slowly. I’m gonna give a force and propeller will spin as much as that force than it’s gonna stop, slowly.

I did:

float adf = (Mathf.Abs(startPoint.x - endPoint.x)) + (Mathf.Abs(startPoint.y - endPoint.y));    
rotZ += rotationSpeed * adf * Time.deltaTime;    
transform.rotation = Quaternion.Euler(0, 0, rotZ);

But it’s spins forever. I want to make it spin as “adf”

Try replacing the += with just =

+= adds to rotZ, so even if it was greater than 0 for just a single frame, it will always be greater than 0, and will never stop.

= replaces the value in rotZ with whatever is after the sign, it can stop if you set it (or adf in your case) to 0