You cannot partition a volume. You must partition a drive (device). To do so, click on the drive itself, located just above the partition you selected on the sidebar ("Samsung Portable...").
Then, you can partition the disk.
Edit: Back all data you want to keep up and Erase the disk as GPT (GUID Partition Table). Newer versions of DU for some reason don't ...
This will clear all the data on your drive!
You can erase the whole volume by clicking the View button and choosing Show All Devices. Then select the top-level entry and click Erase. Set it to APFS and GUID and click Erase. Name it Macintosh HD (or whatever you prefer if that's not your preference). Then run the installer on your new Macintosh HD and you'll ...
Your disk has a capacity of 250.69 GB with 211.9 GB used leaving 38.8 GB. The reported free space is 74 GB but 37.5 is purgeable. Purgeable space on a Mac is space that the Mac considers save to clean up. So while it says you have 74 GB available, 37.5 GB is currently in use but is safe to erase and clear off..
and I get "disk out of space" on a Terminal where I copy the files with cp -r.
I suggest using the ditto command. You can use ditto to copy directory to directory. It includes all nested directory. No idea how links would work.
Would the source disk be timemachine disk? It uses hardlinks which result in a copy of the data being made for each hardlink.
Unlike some installations of some operating systems there is no OS level uninstall feature in macOS.
That is true for applications, though some do have uninstallers available.
That is true for minor OS version upgrades, EG 10.14.1 to 10.14.2
That is especially true for full versions, EG 10.14 to 10.15
What that means is that if you install an OS update ...
I ran into this same issue trying the same thing on Mojave. It appears that ACLs on symlinks just aren't supported when working within the confines of disk images. I did come up with this workaround though:
Create a blank sparse image that's big enough to hold the backup.
ditto the backup directory into the mounted sparse image. It will make the same ...
Please note that although both outcomes are the same whether encrypting with Disk Utility or Time Machine, Disk Utility takes significantly longer.
Perhaps this is because it is encrypting the unused free space and TM is not.
Can anyone else corroborate?
Also, in Terminal you can simply use this command to show TM volumes & status:
diskutil cs list