iPhone 17 iCloud backup size inconsistent with Photo Library

I recently upgraded from an iPhone 12 to an iPhone 17 and restored from my iCloud backup. Everything seemed to transfer successfully - all my photos and data are on my new phone. However, I'm seeing very confusing and inconsistent backup size numbers that don't add up, and I'm trying to figure out if my photos are actually backed up or if this is just an iOS 26 display bug.

On my old iPhone 12, my iCloud backup was 10 GB. I had iCloud Photos turned OFF (intentionally using iCloud Backup instead), and everything worked normally with no issues. When I got my iPhone 17, I restored from that backup and kept the same setup - iCloud Photos is still OFF on the new phone.

Here's where things get confusing. When I go to Settings > [My Name] > iCloud > Manage Account Storage > Backups > iPhone 17, it shows my backup size as 2.17 GB, with a "Next Backup Size" of around +66 MB. But when I scroll down to the list of what's being backed up, it shows "Photo Library: 7.83 GB" with the toggle turned ON, plus about 800 MB of other apps. The math doesn't work - how can a 2.17 GB backup contain 7.83 GB of photos plus other data?

When I look at the main iCloud storage screen (Settings > [My Name] > iCloud > Manage Account Storage), it shows my total iCloud usage is 5.4 GB, with "Backups: 2.2 GB". This is drastically different from my old iPhone 12's 10 GB backup, even though I have the exact same data on both phones.

What really concerns me is what happened when I deleted my old iPhone 12 backup. My total iCloud usage dropped from around 15 GB down to 5.4 GB - a drop of almost 10 GB. This suggests that the photos from my old backup weren't actually transferred to the new iPhone 17 backup, and I may have just deleted the only copy in iCloud.

I've tried manually running "Back Up Now" several times, and the backup completes successfully, but the size never changes. Photo Library is definitely toggled ON in my backup settings. My iPhone 12 on the older iOS version showed backup sizes correctly and consistently - it was a straightforward 10 GB. But now with iOS 26 on the iPhone 17, I'm getting these confusing inconsistent numbers that don't make sense.

My main questions are: Are my photos actually backed up? The backup details screen says Photo Library is 7.83 GB and toggled ON, but the total backup size of 2.2 GB suggests they can't possibly be included. Is this an iOS 26 display bug? If I were to restore this backup to another iPhone, would all my photos actually be there, or would they be missing? Why does "Photo Library: 7.83 GB" appear in the backup details list if it's not actually included in the 2.2 GB total?

I'm running iOS 26 (latest version) on my iPhone 17 with a 50 GB iCloud storage plan.