What's the best way to recover data from corrupted iPhone 6s (iTunes not working/iCloud not used) What has happened... the timeline:

29 Nov around 23:00 :   iPhone 6s full backup encrypted

30 Nov around 07:00 :   iPhone 4s synched (backed-up automatically in the process / incremental backup)

30 Nov around 18:30 :       iPhone 6s full backup encrypted

Around 30 Nov 22:00  :      Need to recover the iPhone 6s

29 Nov backup not visible on the backup list !

30 Nov 7:00 can be used but it recovers 4s backup onto 6s (included 6s app and some - not all - 6s data)

30 Nov 18:30 visible but when try to recover it says its corrupted operation failed (seems like my backup got mixed up)

I also have backup of iPhone 6s from 27 Sep, it works as well but when used I get again everything. I recovers iPhone 6s data and applications and iPhone 4s (applications)!

I can clean up the Sept 27 recovery but really need notes from Nov 29/30.
Is there a way to move them (backup files to a backup that works from 27 Sep)

If not are there tools to recover data?

I have found:

https://drfone.wondershare.com/ios-data-recovery.html

https://www.iphonebackupextractor.com/register/

Are there reliable/clean?

Appreciate any help!

Best regards,
Damian 

PS. All backups are local iTunes based.
If you only need to get the notes from your backup, just download third party application to extract your notes from the Backup ( but if that is encrypted, most softwares ask to decrypt the backup first. So I assume 27th November backup is not encrypted) 

After the extraction of Notes from backup, restore 27th November backup to iPhone and import those Notes from the PC (Which you are extracted from backup) 

Import notes from PC : https://support.apple.com/en-gb/HT205793

It is not quite possible to repair a corruped iTunes backup because mainly those are encrypted. So you best shot is what I described. 

I think you have asked that whether these provided links applications are reliable and clean. I've used DrFone program personally and that wasn't quite satisfying. But that could be great for you since that has good ratings. Give a try to find out which program is the best for you to do your task.