Troubleshooting & messages · Moves and copies that didn't finish
Why won't Storage Studio move my Photos library automatically?
Short answer: If the drive isn't connected when Photos opens, Photos starts a new empty library, so Storage Studio never moves it automatically. Use Apple's own method if you want it external.
If the drive holding a moved Photos library isn't connected when Photos opens, Photos starts a brand-new empty library — which looks alarming and can lead to confusion about which library is which. So Storage Studio never moves it for you on its own.
If you want your library on an external drive, Apple's own method is to move it in Finder and then open it with Photos while holding Option. Keep that drive connected whenever you open Photos — Apple's Photos help describes the steps in full.