A20 is currently on Unity 2020.3.1. I'm currently on 2020.3.10 for testing. A20 will probably end up on a slightly newer version than that.
None of that means DX12 or Vulkan will be working great. Unity may have fixed issues, but there can easily be more. In the Unity editor, on the version I am testing, DX12 started to have a huge drop of 40 FPS, so I went back to DX11 and it was fine. There is a reason they still have DX12 marked as Experimental.