since 3.2 im running into this error everytime i run a Game, even a new Project without touching anything is showing me this. I reinstalled Unity, didnt help either.
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.ObjectSelector.OnDisable () (at C:/BuildAgent/work/f724c1acfee760b6/Editor/Mono/ObjectSelector.cs:138)
I finally figured out what the problem was. The old window layout format doesn't support the new Object Selector; to make the error go away, just do Window>Layouts>Revert Factory Settings.