iPhone 14 system data rapidly filling storage

When system data swells, it's almost because you have some corrupt data there. It's actually pretty easy to fix and that is by backing up your iPhone, then restoring your phone from backup. System data will return to normal levels after doing this. See how to do that here --> Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

"Same here with an iPhone 16 / iOS 26.2, and reset doesn't really help, as it will grow back. Wondering if anyone find real solution yet."

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System Data Consistently Returning:

Clearing System Data: How to Clear "System Data" in your iPhone's Storage: - Apple Community

I'm not having this issue with my iOS at the moment, but one of my Macs is, and I just cleared the System Data on it with Apple. So, there's something going around; likely a glitch in the software update where items are being configured slower. When caches are created, the System Data increases. The Operating System needs to get its apps ready for things so that they can open faster and operate more efficiently. But, with lagging, System Data is not being taken care of fast enough. So, report this to Apple:

Reporting this to Apple:

Do your Part: Provide Apple with feedback on this, letting them know about this issue.  Apple may not get back to you directly, but the more feedback they receive on this, the more they will know what is occurring, and what bug fixes to include in updates to come. Apple will know nothing of this, if you don't report it to them.

1. Go Here: Feedback - iPhone - Apple
2. Select: "Bug Report" for the "Feedback Type"
3. Comment: that this all began after installing an update. Include the URL of this thread.
4. Proceed from there as necessary

"iPhone 14 system data rapidly filling storage: I backed up everything to iCloud then wiped my phone then signed in again and it’s working well now! The system data is no longer taking up that absurd amount of storage space."

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Excellent job troubleshooting this!

For anyone out there wanting to fix this, wiping an iPhone without first backing up you data is not a wise decision. So, do as instructed by the OP and back this up to iCloud, first: How to back up your iPhone or iPad with iCloud - Apple Support

Report this Bug and Fix to Apple:

Do your Part: Provide Apple with feedback on this, letting them know about this issue and the solution.  Apple may not get back to you directly, but the more feedback they receive on this, the more they will know what is occurring, and what bug fixes to include in updates to come. Apple will know nothing of your findings, if you don't report it to them.

1. Go Here: Feedback - iPhone - Apple
2. Select: "Bug Report" for the "Feedback Type"
3. Comment: on the issue, and the solution. Include the URL of this thread.
4. Proceed from there as necessary

Same here with an iPhone 16 / iOS 26.2, and reset doesn't really help, as it will grow back.

Wondering if anyone find real solution yet.