Think the answer may be in the word Radeon, i.e., AMD as this is the same with an AMD RadeonPro XT5700 16Gb card described by Apple as being a GPU... only the CPU option shows up in FireFly with this card too. I would suggest raising a ticket with support https://support.posersoftware.com The more Macintosh users that complain the more likely it will be considered as something requiring a fix..