Does iTunes back up a complete image of a device or only Apple's apps and data?

rfritchman wrote:

I have 500 GB of video data stored in my iPad's "Infuse" video player app and it doesn't appear to be backed up anywhere.

The issue is moving that data (which appears in iTunes in the "File Sharing" setting) to a new iPad. Air-dropping it moves it to the Files app, not the "Infuse" app.

I see this in support.apple.com but can't believe it's true:

"A backup from a computer doesn't include: Content from the iTunes and App Stores, or PDFs downloaded directly to Apple Books. Content synced from your Mac or PC, like imported MP3s or CDs, videos, books, and photos."

What's the point of a backup if it doesn't back everything up? And what's the point of the QuickStart migration if it doesn't migrate everything? How do you move sync'ed content?

Your confusion is thinking syncing and backing up are the same thing, there is a big difference.

What is sync isn't part of the backup as outlined in your thread "contents synced". Backup methods for iPhone, iPad, and iPod touch - Apple Support

Their website makes no mention of backing up data, only syncing data as outlined here https://support.firecore.com/hc/en-us/sections/4405016246295-Keeping-Things-in-Sync