For removable media, I believe that finishing up with "eject" would be the safest way to ensure that all writes were committed to the hardware.
("Eject" is macOS's term for "unmount filesystem")
"eject" is a Linux command which attempts to safely disconnect removable media.
https://manpages.ubuntu.com/manpages/noble/en/man1/eject.1.h...
TFA doesn't mention filesystems at all, sort of jumps in where we find the block device. Things could become messy if the device were mounted while the copy is attempted.