Photos library will not open (4302)

This problem has come up before on Apr 11, 2020, and the answer given then was:

• Copy the library to be imported onto the hard disc
• Hold down the Option key while starting Photos, and from the dialogue box select the new library
• Then press and hold the Command and Option keys while clicking Choose Library.

I have tried this, and it attempts to repair the library. However, once the progress bar reaches 100%, the library still cannot be opened and the same error message is given.

I am trying to move a photo collection

• from an iMac running Kernel version "Darwin 10.8.0"
• to a newer one running BigSur.

The library was restored to the new machine from a TimeMachine backup taken on the old one. It contains thousands of photos and has a size of 128 GB.

The fallback position would seem to be to "Export" all the photos from the old machine, then import them into the new Photos library. This is not an appealing prospect because of the large volumes of data, and furthermore I am worried that the Creation Date and Modified Date would be lost.

From within Finder, I can navigate to the new library and "Open package", and within the library I can see folders for "Originals", "Modified" etc. What would happen were I to try and import the individual files from the "Modified" folders? Would that:

• bring across all the photos in their post-editing state?
• would it also bring across photos that have never been edited?
• would they retain their dates?

Guidance would be appreciated.