It seems that you are having trouble opening your Photos Library on your Mac. One possible reason why you are seeing the error message "The library could not be opened. Photos was unable to open the library "Photos Library". (4301)" could be due to a corrupted library file. You can try repairing your library by following these steps:
1. Quit Photos.
2. Press Option-Command and double-click the Photos icon in the Applications folder (or click the Photos icon in the Dock).
3. In the Repair Library window, click Repair to rebuild your photo library.
If this does not work, you can try restoring your library from a Time Machine backup. It is important to back up your photo library before repairing it.