I want to edit my pics with nitro
Then select a subset that I marked as favorite
Then copy those into a shared folder
This seems to take a few extra steps because I have to go first to a regular iPhoto folder, which is tricky, and then go to iPhoto and copy from that folder to the shared. Is there a better way?
If you are trying to add images to a Shared Album, then that has to be done in Photos. Apple does not provide an API for third parties to manipulate shared albums.
Another approach is to use the Flag feature of Nitro and then find the flagged album in Photos (it’s inside the Nitro folder). Then share those.