Why the extra step when opening Photos - High Sierra

If it is not a problem of the file system format, try this:

If I remember correctly, there has been a problem with broken Photos Preferences or broken Home folder permissions after the High Sierra update. To force Photos to update the preferences it helped in some cases to create a new Photos Library in the Pictures folder, then switch back to the correct library. To create a new library and switch between libraries, see: https://support.apple.com/guide/photos/create-additional-libraries-pht6d60b524/3.0/mac/10.13

Is your Photos library still in the default location (in the Pictures folder in your home folder on your system drive), or have you moved it somewhere else?

If you have moved it off of your system drive, is it on a local (non-network) drive formatted as HFS or APFS?

Photos is looking by default for your library in the Pictures folder, not in the Home folder, so I would move the library back into the Pictures folder.

Since switching between two libraries did not fix the issue, you may want to try to repair the permissions on your Home folder, unless Mark has a better idea.

Have you designated a library as the System Photo Library? I think I recall that one past release used the lack of that designation as meaning you were new to Photos.