2013 Mac Pro with 2.7Ghz 12 core E5 + dual D300
macOS 10.15.3 beta
Blender 2.82 beta
Blender Benchmark 2.80
Blender by default doesn't recognize my GPUs as rendering devices.

I have tried Radeon ProRender, it sort of works, but crashes way too often (from every few seconds to every few minutes), it also limits the numbers of available shaders to about half.
Shaders when Cycles selected as renderer:

Shaders when ProRender selected as renderer:

So at this point, it's not really usable...
Then today, when I tried Blender Benchmark for the first time, I realized it actually recognized my GPUs! Although only one of the 2 GPUs was working during the benchmark, but it totally recognized them.

Now here's my question, assuming Blender Benchmark uses the same rendering engine as Blender, is there any way to get Blender itself to recognized my GPUs as rendering devices?
Thank you in advance for your kind help!