I did have the same problem with the Inpatient tool being greyed out under edit. The inpatient function is used to remove unwanted objects. The getting started tutorial shows it being available on the left side bar tools but it has moved so this tutorial needs updating. Here is the link to getting started tutorial that needs updating: https://vimeo.com/channels/875980
It is now part of a Bush tool on the left side down low (Healing, Patch, Blemish, Inpatient and Red Eye) and it does work. I think that Edit/Inpaint tool on the dropdown menu is used to remove objects from a stack of photos which is actually very cool. So unless you have multiple images it would be greyed? See Inpatient tutorial here for single photo: https://vimeo.com/channels/875980/130966523
Inpainting is also part of the plugins to Apple Photos.
Loving the software
Fred
