Deduplicatation - btrfs

I have 8 windows 10 computers I want to backup as images. Installed debian 11 on a single drive with btrfs (Part structure: efi 5oomb, 4gb swap, remaining btrfs). After client install and successful image backup I have 8 full size images. I then started fresh and installed on only 1 machine & let it image that. I then renamed the machine and let it run the images on that. I was expecting on large/original backup image and the second very minimal as they are identical.

What am I doing wrong? Shouldnt the dedup remove/link all the backed up files that are the same across all the clients?
Do I need to add subvolumes to make it work? On the debian install I did an expert install and choose to configure partitions manually and choose btrfs for the file structure. Do I need to install some kind of btrfs deduplication tools as well?