I am trying to understand why sometimes my Angle value is greyed out under Auto Smooth in the Data Panel of the Properties Editor. Does anyone have any idea why this happens, what it means and how to fix it so that it isn't greyed out anymore? For me this has nothing to do with Sculpting or being in Sculpt Mode. This happens randomly while performing regular poly modeling with booleans in Blender or when importing objects from other 3D packages.
Go to Properties editor > Object Data panel > Geometry Data and click on Clear Custom Split Normals Data to re-enable the angle setting.