Why is my iPhone 16 Pro stuck uploading photos to iCloud?

First, confirm you have enough iCloud storage to be able to upload all photos. Learn more about iCloud storage and device storage and Set up and use iCloud Photos are helpful links.

Try pausing iCloud uploads.

• On your iPhone, iPad, or iPod touch, open the Photos app, go to the Library tab, and tap All Photos. Then scroll to the bottom of your screen.
• On your Mac, open the Photos app. Select Library 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.

Check to see if any other iCloud services are working as expected.

Have a good one

- Noah

Here's a helpful similar post to yours:

Photo upload to iCloud stuck - Apple Community