That's greyed out because you obviously cannot add photos TO All Photos FROM All Photos, because they are already there. Please explain what exactly you are trying to do and we will then be able to help you.
If you are trying to add photos to Lightroom from the Apple Photos app, you would use the "From Camera Roll" option.
I'm trying to add new photo to lightroom. When I choose the "From Camera Roll" option, I don't see all photos in my phone. When I chose one photo from library, I see an error (screenshot in the attachment).