Which library file did you copy from the Time Machine backup?
It needs to be an item with the filename extension ".photoslibrary" and the icon with a fan of three pictures with the rainbow flower. And you cannot simply copy the photos library from Time Machine, you need to run Time Machine and restore the library. To restore with Time Machine:
- Quit Photos if it is running
- Open the Pictures folder in the Finder.
- With your Pictures folder as the front most Finder window launch Time Machine.
- In the time tunnel in Time Machine go back to the date with the Photos Library you want to restore by clicking into the Time Line at the right border of the window.
- Select the Photos Library and click the "Restore" button.
Once the library has been restored, select it in the Finder and double-click it to open it in Photos.