Thank you for the valuable advice on a possible way to create an image on the first partition of the sdd, in order to run the operating system from it…
The reality is that I am not presently knowledgeable enough to get your advice to work properly (even though my main operating system at home is Ubuntu 20.04). And, no, I don’t need the partitions to be formatted as EXT4. It is a matter of wanting the second partition to be accessible for storage by other users, not just for running the system.
Today, I reformatted the whole sdd (a few times) including formatting the first partition to btrfs format. Once I did so, I lost connection with that partition outside of the command line terminal. For example, Ubuntu would not recognize the partition via the file manager.
I think that I am missing something so basic but critical piece that could make things work.
I see a possible approach as described in: Trying to install Freedombox onto Cubietruck SSD - #3 by sunil. But, I am using a WD sdd and not the cubietruck.
Your more basic level of help would be appreciated in knowing how to transfer the image successfully to the first sdd partition.
In step 3, I see two commands in FreedomBox/Download - Debian Wiki
(1) $ dd bs=1M if=freedombox-stable-free_buster_cubietruck-armhf.img of=/dev/sdg conv=fdatasync status=progress
(2) $ cat freedombox-stable-free_buster_cubietruck-armhf.img > /dev/sdg ; sync
I tried both without success. What I appear to be missing, I think, is likely the initial format for that partition and/or some other setting up steps that may be needed.
Thank you in advance for any advice.