It comes from this topic and a moderator has suggested me to make the feature request in this subforum:
For those of us who have a large amount of files on HFS+ format disks and the migration is not easy, it would be very useful if Roon Rock would enable writing to HFS+ disks. This is possible with some apps and Linux distributions. The Rock features page doesn’t differentiate between the abilities of some filesystems and others, however it seems that only HFS+ is allowed to read. If this could be fixed, it would make it easier and happier for more users.