Replace loopN with loop number listed with partx
command
balena os download raspberrypi4-64 -o rpi4.img
losetup -fP --show rpi4.img
mount /dev/loopNp6 $MOUNTPOINT
If the mount fails with wrong fs type
or similar, this is most likely because the image is a flasher image (i.e. for Intel NUC, for example), and you will need to do the following: