dmk0

@Frank1940 As you've been with me through the whole journey: I have finally found the culprit and the solution.
 
After doing a quick google search (again) I stumbled upon this post
This caught my eye but led me in a strange direction. I am not great with managing zfs and I already stumbled because of step 1. Thus, I consulted the discord channel where I got into a dialogue with @jcofer555 (thanks again) reiterating my problem. And at some point mentioning that maybe it could be zfs. I also finally found out what the bash process is: it's the terminal! So, killing it, just closes the terminal
 
Now, experimenting with zfs commands I did the following:
root@Ymir:/mnt/user/data# zfs list -r NAME USED AVAIL REFER MOUNTPOINT disk1 9.07T 7.16T 112K /mnt/disk1 disk1/.Trash-99 96K 7.16T 96K /mnt/disk1/.Trash-99 disk1/data 9.07T 7.16T 9.07T /mnt/disk1/data disk1/data/Download 96K 7.16T 96K /mnt/disk1/data/Download disk1/isos 96K 7.16T 96K /mnt/disk1/isos disk1/other 2.18G 7.16T 2.18G /mnt/disk1/other disk2 9.06T 7.17T 96K /mnt/disk2 disk2/data 8.75T 7.17T 8.75T /mnt/disk2/data disk2/data/Download 120K 7.17T 120K /mnt/disk2/data/Download disk2/other 317G 7.17T 317G /mnt/disk2/other disk3 8.86T 7.37T 104K /mnt/disk3 disk3/data 8.67T 7.37T 8.67T /mnt/disk3/data disk3/other 196G 7.37T 196G /mnt/disk3/other disk4 1.75T 14.5T 112K /mnt/disk4 disk4/data 1.72T 14.5T 1.72T /mnt/disk4/data disk4/other 24.5G 14.5T 24.5G /mnt/disk4/other disk5 2.66M 5.33T 96K /mnt/disk5  
Combining this with the above post, I just tried to do a
zfs destroy -r disk1/data/Download Which removed it from the list once. I did it again for disk 2. Now the list was empty. I went into the share and the folder was finally GONE.