Google Photos has received a burst of updates over the last weeks. It keeps changing, and Google do not inform what they change when an update arrives in Play Store. Maybe the information can be found elsewhere, but there is not much we can do when Google decide to remove features and change their app.
The movie assistant in Google Photos currently has other show-stopper issues for me. I added a comment to a thread in Google's support forum:
I use the kdenlive.org video editor on the computer until it is sorted out.