How to get amdgpu dimgrey cavefish working?

I have a Radeon RX 6600 which to my understanding is Navi 23 / dimgrey 
cavefish.

I have built drm-kmod using poudriere, which also got me 
gpu-firmware-amd-kmod-dimgrey_cavefish.

I have run `kldload amdgpu`, as well as added it to kld_list in rc.conf

When I run `startx` I get “Cannot run in frame buffer mode. Please 
specify busIDs for all framebuffer devices.”

I’m not sure what to do. I believe my car is dimgrey cavefish, and I 
have the dimgrey cavefish drivers.

How do I load / use them?

Pat