I have installed dietpi with nextcloud I have a 120G miro SD card that has the image on it and I have it up and running.
I have went into the dietpi and confirm the disk are mounted (4) 2TB SSD, they are not being seen on nextcloud its only showing my SD card total space.
I tried to format the disk to ntfs and EXT4 did not change anything.
These harddrives are in my QUAD SATA KIT FOR RASPBERRY PI 4
The link below is the specs of the unit
I should note I am able to access the NextCloud via phone and computer web portal to upload items. But for some reason I think something in dietpi might not be correct.