Have you verified that after updating not all photos appear? The photos that you have saved in iCloud, and which you can access through your iPhone's library, may be downloading again after the update. Therefore, they should appear in a few minutes, although the time may vary depending on the number of photos you have stored in iCloud. If after a while they don't appear, follow these steps.
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Check that you have the option of 'Photos in iCloud' activated. You can do it in Settings> Forums> iCloud.
- Restart your iPhone and check if the images already appear after starting