System Data issue iOS 26.2

A couple of points:

• Offloading apps only removes the app and the data is still stored on the device. To truly remove the data including the cache and system data used by those apps, you have to delete them, not use the Offload option.
• Optimized Storage of your photos is working correctly. Your entire photo library is not stored in iCloud and your device will still store the lower resolution versions of those photos to be viewed in the Photos app. With over 71,000 photos, having only 18GB stored on your device is very good.
• Do you have WhatsApp installed?
• Did you restore your phone using a computer as opposed to on device referred to in your linked article? I would recommend doing that after deleting the unused apps. 166 apps is a lot and they each have cache data stored by the System.
• Instead of using the simple restart, try using the Force Restart that will also help clear additional cache data. When following the steps here, it could take up to 15 seconds before you see the Apple logo and release the side button. You have to ignore anything else you see on the screen during that time and if you do not see the Apple Logo, try again as it may take a couple of attempts to get the speed and sequence of the key presses correct.

Force restart iPhone - Apple Support

• Restart the device. That's it.

If the above does not resolve the issue then...

I would ignore that because this system data will make room when you need more space on your iPhone. These are some cache and temporary files that will be erased by the system whenever you try to save more files.

You may --> Clear Other storage on your iPhone or iPad - Apple Support (IN)

Tap on System Data it will take you to "Other System Data"

Now the question is what is the "Other System Data" storage. Read on...

• Other System Data: Non-removable mobile assets, like Siri voices, fonts, dictionaries, non-removable logs and caches, Spotlight index, and system data, such as Keychain and CloudKit Database. Cached files can't be deleted by the system.
• System: Space taken by the operating system. This can vary based on your device and model.

About cached files in "Other System Data"

Finder and iTunes categorize cached music, videos, and photos as Other instead of actual songs, videos, or photos. Cached files are created when you stream or view content like music, videos, and photos. When you stream music or video, that content is stored as cached files on your device so you can quickly access it again.

Your device automatically removes cached files and temporary files when your device needs more space.

If storage on your device differs from what you see in Finder or iTunes

Since Finder and iTunes categorize cached files as Other, reported usage for Music or Videos might differ. To view usage on your device, go to Settings > General > [Device] Storage.

If you want to delete the cached files from your device

Your device automatically deletes cached files and temporary files when it needs more space. You don't need to delete them yourself.

I would ignore that because this system data will make room when you need more space on your iPhone. These are some cache and temporary files that will be erased by the system whenever you try to save more files.

"System Data issue iOS 26.2: My iPhone 15 Pro Max 256 GB running iOS 26.2 is eating up all my storage. It has consumed 130 GB of "System Data". Every time I free up data from my apps, the System data consumes the free space. I cannot remove or reduce the System Data size. Apple Photos will also not 'Optimise iPhone Storage' - it remains at 18GB"

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Clearing System Data:

Use my User Tip: How to Clear "System Data" in your iPhone's Storage: - User Tip