iTunes could not restore the iPhone...?

I consistently get this error when attempting to restore my iPhone X from an encrypted iTunes backup on a PC (windows 10).

Currently I'm looking at losing 2 years of data, most importantly photos.

The Phone is updated with the latest version of iOS (15.1)

I've uninstalled and reinstalled iTunes.

I believe the backup was created on the iPhone X before upgrading to iOS 15 or was an iOS 15 backup created on an iPhone 13 pro which I had to return.

I've tried:

• Restoring over another back-up (my iPad and my wife's old backup, both these backups restored without issue.)
• Restoring after a full reset
• Restoring through recovery mode

I receive the same error every time.

3rd party iPhone backup extractors show my data is intact and can be extracted but not for free.

I've unsuccessfully attempted to downgrade the iOS to iOS 14 but get 3194 error each time.

I there anything else I can try?

Or some way I can extract 5000+ photos and videos for free?

Thanks for your help.