1) you have to decompress the .xz to flash the .img
2) give an 'lsblk' command to see whether the /dev/sdc is mounted to any directories, probably 2
3) if yes, unmount with 'umount full-path-to-directory' for all directories
4) now flash the .img
if your application decompresses automatically the image then you can skip step 1
it is useful to learn to do it fundamentally through the terminal with he following command
'sudo dd bs=1M if=image-file of=/dev/sdc status=progress conv=fsync'
that is dump the binary data in 1MB blocks from the file to the eMMC showing the progress of the operation and flushing the buffer
2) give an 'lsblk' command to see whether the /dev/sdc is mounted to any directories, probably 2
3) if yes, unmount with 'umount full-path-to-directory' for all directories
4) now flash the .img
if your application decompresses automatically the image then you can skip step 1
it is useful to learn to do it fundamentally through the terminal with he following command
'sudo dd bs=1M if=image-file of=/dev/sdc status=progress conv=fsync'
that is dump the binary data in 1MB blocks from the file to the eMMC showing the progress of the operation and flushing the buffer