Photos app cannot load library even when creating a brand new libiary

It would be good to know a bit more about what is happening. Where are your libraries-- in the Pictures folder or on an external drive? Has this worked before, and the behavior is new? Anything changed? How are your Photos preferences set? Specifically,

In Photos>Preferences>General,

Is "Use as System Photo Library" grayed out (indicating it is) or solid (indicating this isn't your system library)?

Is "Copy Item to the Photos Library" checked? (This is the default, indicating a "Managed Library")

In Photos>Preferences>iCloud

Is "iCloud Photos" checked?

If it is, is "Optimize Mac Storage" check?

Before we get more information, we can suggest you try these things:

• Restart the computer (of course)
• Rebuild your Photos Library--close Photos and re-launch by option-command-clicking the app icon.
• Make a new user and see if the same problem recurs with it
• Use another library if you have one, or make a small test Library with a few pictures in it and see if the same thing happens.
• Start in Safe Mode (different for different computers) This bypasses certain potentially disruptive processes.

           Start up your Mac in safe mode - Apple Support 

One of these steps may fix the problem, but their failure to work is also diagnostic.

Have a Happy New Year!

Could you let us know about the other things? You mentioned an external drive-- how is that formatted? It must be formatted in either APFS format or Mac OS Extended (Journaled) format.

Have you been using Photos before? Is the behavior new? Anything changed? Did you try re-starting in Safe Mode? What happened then? Did you try creating a new user and logging in there? Have you used any system-wide 3rd party software like virus checkers or drive cleaners?

It's hard to help without knowing the answers.