So today I tired #mkfs.btrfs and this works. I was using #gparted, which can’t create #encrypted file systems and so I created a blank (cleared) one, used #cryptsetup to create the #encryption on the device, and then created the brtrfs file system.
@mkwadee
It sounds as if you made a good choice. Ext4 uses a journal and will wear out a USB data stick prematurely by writing to the same blocks over and over again. (For this reason, I generally use Ext2 on data sticks.) A brief Web search suggests that btrfs is more flash-friendly than Ext4.
@CppGuy Thanks, I didn't even consider the wear-out issue.