title: The Canvas Environment on my Prefab is greyed out in the Unity inspector, what have I done?
body: <p>I have made a prefab that also had a canvas. Unity added a Canvas Environment as the parent.
  Never had an issue until today. For some unknown reason, when I try to edit the prefab, the Canvas Environment is greyed out and not ticked in the inspector, and I am therefore unable to see any of the prefab in edit mode.
  I am unable to tick it in inspector to activate it.</p>
  <p>Any ideas? It has happened to all prefabs that have a Canvas Environment. What have I accidentally done :(</p>
  <p>Version 2019.3.7f1
  Picture of inspector: <a href="https://ibb.co/FJSz79q" rel="nofollow noreferrer">https://ibb.co/FJSz79q</a>
  Picture of Prefab hierarchy: <a href="https://ibb.co/bm6NbhL" rel="nofollow noreferrer">https://ibb.co/bm6NbhL</a></p>