on the last step, can you please double check disk usage of sd.img? are there files in it? (if you already have sd.img skip creating again and start with kpartx) when mounted run df -h /media/xubuntu/fa6c4c4c-846e-4c6f-8c02-e93cf5ebf448 or find -type f /media/xubuntu/fa6c4c4c-846e-4c6f-8c02-e93cf5ebf448

I can see in the phone system root folder in the phone. And it has only 203 MB as well. My concern is...if I "forget" the SD card, will I lose the files from the "phone" internal storage? Because right now I can't access the phone internal storage. I can only see the system folder. But I can see the folders in the adopted SD card (which are almost empty).

but what about the files in sd.img?

Size: 30G | Used: 239M | Avail: 29G

Could it be that it was saving most of the data (or all of it) in the internal phone memory instead of the SD card even though they are both integrated? But now my files are being held hostage in the phone memory. If I want to "unlink" or "unadopt", what are my choices? From what I can see, there are 3 ways...1) insert a new SD card and adopt it as internal storage WITHOUT "forgetting" the first SD. 2) "Forget" the adopted SD 3) "Migrate" the files from the internal storage option (even though it says "it will free 0 bytes on SD card"). And then "format" the SD card as portable". Which one?

if 1) is possible that seems the best option

you should run extundelete or testdisk or photorec or binwalk on /dev/mapper/crypt1 maybe there can be some files recovered (search for that keywords here or www)

"Sudo extundelete /dev/mapper/crypt1 --restore-all" ??

yes that will scan for deleted files based on inodes. you can also run these tools on your internal storage data.img

From TWRP?.....

with this tools you can scan your internal storage and your adoptable storage for deleted files as well. photorec is more powerful, binwalk the deepest file search. testdisk has also some options to restore deleted files but that tool is more for repairing partition tables and maybe just as good as extundelete

here is example usage for testdisk (little complicated) the red files on that screenshot are deleted ones android.stackexchange.com/a/219364 see you tomorrow, it's late

I'm running extundelete and it's taking a long time. There is no indication so I have no idea if it's working or it hang.

Where is it created?

check home directory ~/RECOVERED_FILES