The "Bootable" legacy ISO you've used is in fact not bootable, it relies on CDROM emulation provided by BIOS. VMs don't usually do this sort of emulation. If you set the guest OS to something like ...

The virtual machine may fail to boot from an ISO because the boot order prioritizes the virtual hard disk over the optical drive, resulting in a “No bootable medium ...

For reasons more archival than practical, I've decided it's time to make a one-time backup of all my old floppies. While I may not ever need to use them again, I'd like to make .iso copies of my ...