iCloud photos not showing in Photos app on MacBook Pro

First, where is your Library located? Is it in the Pictures folder on your Mac?

Now, some things to check: Is your Library the System Library? See Photos' Settings>General

Here, "Use as Photos System Library" is grayed out, because this Library already is.

The check Photos' Settings>iCloud

to see if iCloud is turned on.

At the bottom of the Library, check to see if the Mac has synced:

To encourage syncing, be sure you have good internet connection, plug the Mac in, have Photos in the background, and leave it alone.

Let us know…