I have a Cezanne CPU/APU (Ryzen -G ) with on-board graphics and a Polaris GPU.
My APU is one-gen/version number ahead of your APU and the GPU is several models behind that. I tried several recent releases of BSDs (Open, Free, Net, Dragon) with the GPU and I've only managed to get the GPU working under Open. The APU works in Windows and Linux while GPU works in Windows, Linux and OpenBSD.