>> According to https://library.morph.zone/Filesystems, this should be possible
>> using (one of) the following filesystems: ext2/ext3, IceFS, ExFAT, NTFS-3G

> IceFS is the only "viable" option in that it will work [...].
> The other options are either read only or you will need a
> super secret password to gain access to a FS that doesn't exist.

All of the 3 other options do exist and are read+write (see MorphOS Library link above).

ext2/ext3: built-in (MOSSYS:L/)
ExFAT: https://www.morphos-storage.net/?id=1533154
NTFS-3G: https://www.morphos-storage.net/?id=1533155

> IceFS will get corrupted within a month usually and will require
> a reformat since the tools are not very successful at recovery.
> IceFS does not like high volumes of reading/writing.

These issues shouldn't matter for the purpose of downloading DVD ISO files and burning them directly afterwards.