I have just updated my mac pro and I have found that Iray does not work I just get a black render

I am using OS Mojave GPU is a Nvidia Geforce GTX 680 4gig

Any suggestions on a GPU that would work with Mojave as it seems Nvidia is no longer supported

Hi I am not a Mac user but I did see some mention in the Daz forums on the Daz website about some issues with Macs specifically in the "Daz Studio 4.14 Pro, General Release!" forum. Also there is a mention or two about some older Nvidia cards no longer supported supported by newer Nvidia drivers.
I hope this helps you

There is a general issue (DS is not compatible with MacOS Big Sur, Daz is working on a fix - which will break plug-ins - that is expected around the middle of next year).

In this case that doesn't apply - it's probably just that the nVidia drivers on your Mac do not meet the minimum required for the updated Iray; unfortunately there is not, as far as I am aware, a fix as nVidia is no longer providing new drivers for the MacOS. Even on Windows I don't think the 680 is supported any longer. One option, space and budget permitting, might be to get a basic Windows box with a reasonable GPU and use that as a self-contained eGPU while continuing to use your Mac for set up and non-DS tasks.