Photo immediately closes after opening

Try opening the library with the Option+Command keys held down to repair the library.

Where has the Photos library been originally? Also on an external volume? If yes, what is the file system format of that volume?

And what happened to the library before you no longer could work with it?

The problem seems to be, that Photos has still the edited versions and thumbnails of the photos, and it has the metadata saved (filenames, size), but the original image files cannot be accessed or found.

This can happen, if the library gets damaged, for example by running cleaning software to remove duplicates, or by putting the library on a volume with an incompatible file system format, or onto a synced volume, like the DropBox. Or the original image files might be referenced outside the library and are really missing.

Where is your library located? If on an external HD how is that drive formatted and connected to your Mac?

How much free space do you have on your boot drive?

Do you have the iCloud Library enabled?

Try the following in order:

As a test launch Photos with the Option key held down and create a new, test library.  Import some photos and test to see if the same problem persists. Does it? (This tells us if the problem is limited to your current library or is more wide spread)

Next, log into another user account, Set up users, guests, and groups on Mac,  and see if the problem persists. (This tells us if the problem is limited to your user account or is system wide).

Boot into Safe Mode (How to use safe mode on your Mac - Apple Support) by booting with the Shift key held down and check there to see if the problem persists.  Reboot normally and test again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing.