iCloud Photos Not Updating

See the article https://support.apple.com/en-in/HT204264

• On your Mac, go to System Preferences > Apple ID. Click iCloud in the sidebar, then select Photos. If you have an earlier version of macOS, go to System Preferences > iCloud. Click Options next to Photos, then select iCloud Photos.

Pause library uploads to iCloud

When you turn on iCloud Photos, the time it takes for your photos and videos to upload to iCloud depends on the size of your collection and your Internet speed. If you have a large collection of photos and videos, your upload might take more time than usual. You can see the status and pause the upload for one day.

• On your iPhone, iPad, or iPod touch, go to Settings > [your name] > iCloud > Photos. You can also open the Photos app, go to the Photos tab, and scroll to the bottom of your screen.
• On your Mac, open the Photos app. Select Photos in the sidebar, then click All Photos in the list of tabs in the toolbar. Scroll to the bottom of your photos and click Pause.

Read the preferences article for photos https://support.apple.com/en-in/guide/photos/pht5156cc968/4.0/mac/10.14

It can take a month or more ( the photos are massive ) , restarting Mac is a very basic solution as suggested make sure you have combined the libraries https://support.apple.com/en-in/HT209528 and using a single photo library and designated https://support.apple.com/en-in/guide/photos/pht6d60b524/4.0/mac/10.14#pht6d605ea2

Welcome to the Apple Community.

What does it say at the bottom of the photos window?

Do you not see a progress bar and a count of how many items are waiting.

Is this a first sync of a large library?

How many items are there? Are any of them videos? Have you restarted the Mac?

(Turning off iCloud will only restart the whole process again)

It depends upon the network speed , connect the Mac with power outlet .