If you try to mount an ISO file (like a Linux distribution) on MacOS and you get that weird error saying “No mountable file systems“:
Then, you can easily find a workaround by using CLI.
% mkdir /mnt/iso % hdiutil attach -nomount FILENAME.iso /dev/disk2 FDisk_partition_scheme /dev/disk2s2 0xEF % mount -t cd9660 /dev/disk2 /mnt/iso
And now, the content of your iso file is available in /mnt/iso directory.
To unmount the ISO file, just type:
% umount /mnt/iso