$ guestfish --ro -a /vzt/images/Rocky-9.3-x86_64-minimal.iso -i
guestfish: no operating system was found on this disk

If using guestfish ‘-i’ option, remove this option and instead
use the commands ‘run’ followed by ‘list-filesystems’.
You can then mount filesystems you want by hand using the
‘mount’ or ‘mount-ro’ command.
.....

$ virt-ls -a /vzt/images/Rocky-9.3-x86_64-minimal.iso /
virt-ls: no operating system was found on this disk

If using guestfish ‘-i’ option, remove this option and instead
use the commands ‘run’ followed by ‘list-filesystems’.
You can then mount filesystems you want by hand using the
‘mount’ or ‘mount-ro’ command.
.....

That seems to be because there's no <root> element in the inspection result:

$ virt-inspector -a /vzt/images/Rocky-9.3-x86_64-minimal.iso

<?xml version="1.0"?>
<operatingsystems/>

Shouldn't we tweak inspect_get_roots() (from daemon/inspect.ml) to
recognize ISO9660 as well?