I have changed my iPhone from iPhone7 32Gb to iPhone7 128Gb. I backed up my old iPhone running iOS 13.5 using iTunes and try to restore that backup in new iPhone running iOS 14.0.1. the problem is that when restore backup process finished my iPhone went into Apple logo boot loop so I have to reinstall iOS 14.0.1 using iTunes. I tried to restore twice but every times I ended up in boot loop problem and have to reinstall iOS. I badly need my WhatsApp data so is there any way or 3rd party application to restore just WhatsApp data from my encrypted iTunes backup?
There is a company called BackupTrans that promises to be able to recover lost data from backups. I didn't try what you are suggesting, but I successfully transfered WhatsApp data from an android phone to iPhones 3 times using their "android whatsapp to iphone transfer" programme. You could try to do some research on their products, maybe there is something useful for your case.