Click on the link to learn how to optimize the storage on a device --> How to check the storage on your iPhone and iPad - Apple Support
- "If your device is low on storage, it automatically frees up space while installing an app, updating iOS or iPadOS, downloading music, recording videos, and more.
To make more storage available, your device can remove some of your items, like streamed music and videos, files in iCloud Drive, and parts of apps that aren't needed. It also removes temporary files and clears the cache on your device. But your device only removes items that can be downloaded again or that aren't needed anymore.
If your iPhone, iPad, or iPod touch won't update read this support article --> If your iPhone or iPad won't update - Apple Support