Hi Neil
I had tried the OVA today with ArcaOS 5.0.8 and it installs with a SATA - AHCI (emulated) CD-ROM.
Try mounting the ISO CD-ROM from the CD icon at the bottom of the VM (Picture Attached), and reboot the VM. The installation process boot file from there, it does not need to be an emulated IDE CDROM, with SATA runs fine.
Regards