Exclamation mark when attempting to open photos in my Mac

So if I understand correctly - you are downloading to your mac, from iCloud. Is that correct.

If so, the sync may be still ongoing. It can take a long time - days, or even weeks for a large library.

What does the status say at the bottom of the all photos view? Here is mine (updated just now)

Please give more details.

What exclamation mark? Where are you seeing it? When. Any error messages? The more detail you give, the more likely it is someone can help.

Also - where is your library stored?