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.