I've just built a PC with a Ryzen R7 5700G APU, and it's working well under Ubuntu 20.04.3 except for the fact that I can't get OpenCL to work.
So far I've mostly tried installing AMDGPU and AMDGPU Pro, and have tried releases 21.30, 21.20, and 21.10, and have tried these on both Ubuntu 20.04.3 and 20.04.2. I also tried AMDGPU and AMDGPU Pro 20.30 with Ubuntu 20.04.1. But no luck with any of these, regardless of if headless or not headless (though not headless breaks the graphics), regardless of AMDGPU or AMDGPU Pro, and regardless of pal, legacy, or rocr. Also tried ROCm, which also failed to work.
With clinfo I can see that there is one platform (the APU), but no devices, thus it isn't usable for any apps that require OpenCL devices. The APU otherwise seems to be working well under Ubuntu 20.04.3 - WebGL in Firefox and Chrome works, and the system recognizes it (albeit as Renoir rather than Cezanne).
If anyone's been in the same situation and managed to get their Cezanne APU graphics working with Ubuntu, I'd love to hear about what worked for you! Or if anyone has any ideas of what to try, or if I just need to wait for future AMDGPU or Ubuntu updates.