There is only mention of DX12.
The current beta build (1.27.18 or 19) has a known issue with DX12 (texture memory corruption/probably GPU driver bug) and Asobo has restricted some features to check the issue.
As a result, DX12 performance on nVidia GPUs is not available.
Asobo has officially announced that both the MSFS software and nVidia GPU drivers will be fixed in the next version, probably the official SU10 version.
2022/09/08 Devupdate blog
Therefore, we do not recommend testing the performance of the DX12+OpenXR combination with the current version. It would be better to wait for a week or so and wait for a newer version.
Of course, there is nothing wrong with testing the OpenXR side.