so i've found the right way to get back all the "deleted" data:
-restart windows to be able to mount the disk
-mount the disk
-launch recovery process once disk fully decrypted.
it worked on the USB Stick i tested + on another old HDD.
But for a reason i don't get, it's not working on the actual disk i wanted to recover.
data is still corrupted even after trying multiple times with the different headers i had backed up, maybe wrong headers or something else went wrong somehow, maybe i did some writing by mistake to the disk after deleting it and it corrupted the whole thing, no idea.
atm i've lost hope for this data, i guess it's gone for ever.
thank you for trying to help me @davidXanatos.