This post briefly describes how to configure a phone installed with Android 7 to only use WiFi for backing up and synchronizing Photos and Videos via the Google Photos.
By Default, WiFi
By default, Android backs up and sync photos and videos automatically via WiFi. In case it uses Mobile Data, the following settings under the Mobile data backup section can be turned off as follow:
Go to Google Photos -> Settings -> Backup & sync -> Mobile data backup.
No WiFi Test
When we open Google Photos, we will see the “Waiting for connection” message.