Photos app stuck on "Restoring"

I think maybe leroydouglas was suggesting that your hard drive may not be formatted appropriately for use with Photos. The link he referenced makes the point that to avoid damaging the Photos Library an external drive must be formatted in either APFS format or Mac OS Extended (Journaled) format. Additionally, the drive can not have had Time Machine on it since it was formatted. There have been so many problems with using incompatible drives that the newest macOSs won't even allow a Library on a non-Mac formatted drive to open, since there is a chance of damaging the Photos database. See this:

Move your Photos library to save space on your Mac - Apple Support

You may also need to check the "Ignore ownership" tag for your hard drive. You can do that by selecting the hard drive and opening the info window with command-i.

This info window will also give the format of the drive.

Let us know what you find...

JarvisHan wrote:

I have been storing my photo library on an external hard drive. As the old external hard drive ran out of space, I replaced it with a new one (LaCie Mobile Drive Secure USB-C 5TB with Rescue). After copying the photo library from the old hard drive to the new one, I was able to open it successfully. However, when I closed the photo app and tried to reopen it, the app got stuck on the 'restoring' screen with the progress stuck at 0%. How should I address this issue?

See if there is anything here—

Move your Photos library to save space on your Mac