Storage grows quickly for unknown document after upgrading to iOS 16

Hello tifrommelville,

This page can help out with managing your storage on the device: How to check the storage on your iPhone and iPad - Apple Support

Use recommendations to optimize storage

In the Storage section of Settings, your device might offer recommendations for optimizing your storage. To optimize your storage:

1. Tap Show All to see all the recommendations for your device.

2. Read the description of each recommendation, then tap Enable to turn it on or tap the recommendation to review the contents you can delete.

Use your device to check its storage

1. Go to Settings > General > [Device] Storage. You might see a list of recommendations for optimizing your device's storage, followed by a list of installed apps and the amount of storage each one uses.

2. Tap an app's name for more information about its storage. Cached data and temporary data might not be counted as usage.

In the detailed view you can:

•Offload the app, which frees up storage used by the app, but keeps its documents and data.

•Delete the app, which removes the app and its related data.

•Depending on the app, you might be able to delete some of its documents and data.

If your device is almost full and can't free up space, you might get a Storage Almost Full alert. If you see this alert, you should check the storage recommendations or you need to offload some less-used content like videos and apps. 

Cheers.