Hi ur57,
The support article If your iCloud Photos aren't syncing to your device offers the following suggestions if that process if not progressing and no error message is displayed to indicate the problem:
"If your photos still aren't syncing to iCloud
Learn what to do if you don't see a status message at the bottom of the Photos app that explains why your photos aren't syncing, or syncing is taking a long time. If you see a Couldn’t Sync [number of items] to iCloud status message, learn how to move these photos to your library.
Connect your device to power
If your device seems to be stuck on a status message that says Syncing [number of items] to iCloud or Syncing with iCloud…, connect your iPhone or iPad to power and to Wi-Fi.
Check your Apple ID
Make sure that you signed in to iCloud with the correct Apple ID on your device.
Learn how to sign in to iCloud
Check which Library view you're in
If you set up iCloud Shared Photo Library in iOS 16.1 or later, iPadOS 16.1 or later, or macOS Ventura or later, check which Library view you're in. When you move photos to your Shared Library, you no longer see them in your Personal Library. You also won't see photos moved to your Shared Library if you're on a device with an earlier version of iOS, iPadOS, or macOS or if the iCloud Shared Photo Library owner has run out of iCloud storage.
Learn how to switch between your Personal Library and Shared Library"
Try those and if still not operating as expected contact Apple Support directly to investigate further.
Regards.