iPhone 13 is laggy after iOS 26.6

You cannot go back.

• When did you update?

After every update it takes about 4 days for the setup to complete the file indexing in the background along with any new object detection algorithms performed on your entire photo library. During this time you should expect increased battery drain, heat, and some lag with your UI until it has finished. Apple provides a Support Article for what to expect after any update here:

About Apple software updates - Apple Support

Specifically for iOS 26.6, Apple states that additional Spotlight indexing is performed in the background to prepare the device for iOS 27, so it may even take a bit longer. For best results, leave your device plugged into power at night.

• What is your Battery Health percentage at Settings > Battery > Battery Health?

If the percentage is below 80% then you need a battery replacement. The battery is only expected to last 500 charges cycles on the iPhone 13 and it would be unusual for it to still be operating efficiently on its original battery. A failing battery is going to struggle with any processor intensive task and only get worse when more depends on placed on it. You would usually see a Service Recommended warning in your Battery Settings once it drops below 80% and that should not be ignored.

No, you cannot downgrade to an earlier iOS version. Apple no longer signs previous releases, so restoring the iPhone will reinstall only the current signed version of iOS.

Emma_ioq7 wrote:

My iphone 13 is laggy after the ios 26.6

Not every issue an individual encounters on their device can be attributed to an iOS update. If the update itself were the root cause, then every device running that same version of iOS would exhibit the identical problem. In such a scenario, the forums would be flooded with countless posts reporting the same malfunction, creating an unmistakable wave of complaints that no one could possibly overlook. The absence of such widespread reports strongly indicates that the issue is not systemic, but rather specific to the device in question.