"documents and data" Itunes storage bar

Maybe one of these articles will help:

https://www.igeeksblog.com/documents-and-data-iphone/

What is "Other" and What Can I Do About It?

Another alternative is to go to:

Settings > General > Storage & iCloud Usage > Manage Storage (under STORAGE)

Then tap on one of the Apps and it will show you how much "Documents & Data" space that App is using. If you want, you can delete the App there and redownload a fresh copy to clear the "Documents & Data" space for that App.

The Document and Data cache can get corrupted and if so the way to correct it is to restore your phone using iTunes. Make sure to backup your device first. This tends to reduce the D&D size but it will start growing again.

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

That accursed bar is known to go way off, in both ways. I prefer to trust what the phone tells me in Settings / General / Storage & iCloud Usage, topmost Storage section.

If you have patience and persistence, you can find out which docs in which app are gobbling space. Just tap Manage Storage in that topmost section, wait for the list to build. Then tap on each item corresponding to an app and you'll see how much space the docs held in the corresponding app's private space are taking. On non-default apps you'll also see the app size itself as well.

There's no automatic system-based mechanism for deleting those docs save deleting and reinstalling the app. You need to visit each and use whatever deletion options the app offers inside. Some are sneaky; WhatsApp and Facebook are known for invisibly caching messages, videos, pictures and requiring jumping a few hoops to get those cleared.