do updates for the iphone affect data usage?

If your asking about cellular data usage, it depends.

If you have an iPhone 12 or newer with a 5G connection and you are updating wirelessly, it will use the 5G cellular to download and verify the update.

If you have a phone older than an iPhone 12 and you're updating wirelessly, the phone will use WiFi for downloading the update and will use cellular data to verify the update but the amount of data that uses is negligible.

Joer205 Said:

"do updates for the iphone affect data usage?"

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What's the model of your iPhone?

Updating Over Cellular:

You can only update over cellular using an iPhone 12 or later with 5G. So, updating over cellular may not be an option for you, if you do not have the corresponding model. See Here: Use an iPhone 12 or later, that is using 5G, in order to update over Cellular - User Tip

Sure. After every update, all data must be re-indexed so things are running in the background and the battery is working hard for a few days after the update until things return to normal.