Hey there que293,
Thanks for reaching out to the Apple Support Communities.
Just to confirm, did you have iCloud Photos enabled on your previous iPhone before creating the backup? If so, photos would not be included in the backup as they would be synced with iCloud.
Check out this link here for more details: What does iCloud back up? - Apple Support
What iCloud Backup includes
Your iPhone and iPad backups include all the information and settings stored on your device that don't already sync to iCloud.
For more details on what to do if you're missing information after restoring a backup, check out this next link here: About missing information after you restore your iPhone, iPad, or iPod touch with iCloud Backup - Apple Support
About your photos
When you use iCloud Photos, your photos and videos automatically upload to iCloud. They aren’t included in your nightly backup. After you restore your device from iCloud Backup, stay connected to Wi-Fi so that your photos and videos can begin to download.
If you haven’t turned on iCloud Photos, iCloud Backup may include photos and videos in your Photos or Camera Roll. Not sure if iCloud Photos was turned on when you made the backup? After you restore your device, check Settings > [your name] > iCloud > Photos. If iCloud Photos is turned on, then the photos were stored in iCloud Photos.
If the photos and videos were included in the backup, they’ll download to your iOS device in the background when you restore. Stay connected to Wi-Fi until the process finishes. The time it takes to restore depends on the size of your backup and the speed of your Wi-Fi network.
Learn more about what's included in iCloud Backup and how to sync photos from a computer.
Let us know if that's able to help.
Take care.