Poser 12 is required for GPU rendering on newer graphics cards.

Turing: 16xx and 20xx

Ampere: 30xx

Was added to Poser 12 according to this post, which also shows how to choose your supported GPU:

http://www.posersoftware.com/documentation/12/Poser_Reference_Manual/Rendering/SuperFly/SuperFly_Render_Settings.htm

http://www.posersoftware.com/documentation/12/Poser_Reference_Manual/Introduction/Welcome/Whats_New_in_Poser.htm