While I'm investigating the root cause, you can try to create a CD-ROM like
this:
qemu-system-aarch64 \
...
-device virtio-scsi-pci,id=scsi0 \
-device scsi-cd,drive=cd0,bus=scsi0.0,bootindex=0 \
-drive media=cdrom,if=none,id=cd0,format=raw,readonly=on \
file=${YOUR_ISO_FILE}
This should give the device the highest priority to boot.
I will check the logic of BDS to see why the order changed.