Unable to open Photo Library after migrating to new iMac
I used Migration Assistant and a Time Machine back-up to move all of my content onto a newly purchased iMac. The Time Machine backup was from my older iMac running Mojave and my content was installed on the new iMac running Catalina. There were no error messages when Migration Assistant was done. Then I updated the OS to Ventura 13.2.1. All seemed fine. However when I eventually tried to open Photos I received the message that
"An error occurred while migrating the photo library"
Although I use iCloud generally, I did not have iCloud activated to back up Photos since my Photo Library is so large (260 GB). I rather relied on the Time Machine back-up on the external drive.
Quit and relaunch Photos did not fix the error. I also tried repairing the library by holding option-command while launching Photos, and this did not work. Restarting in Safe Mode did not get me anywhere.
Now I am trying to use Time Machine to restore the Photos Library from a previous version, but it has been stuck on Preparing to copy "Photos Library" for 24-h. Force quit does not indicate that any open app is not responding, so I did not force relaunch any application. The external HD is connected to the iMac with a thunderbolt 2 cable. How long should I expect this to take? Will it keep preparing when the iMac goes to sleep?
Photos does open on the old iMac (Mojave), although the size of the Photos Library is 230 GB (not 260 GB as on the Time Machine copy?). If I can't restore with Time Machine, would it be advisable to connect the old iMac to the new one directly and manually copy over the Photos Library?
iMac (2017 – 2020)