Windows Mixed Reality OpenXR does nothing with the Oculus Quest 2. That's only applicable to WMR headsets like the HP G2. with msfs2020. I agree that starting up in SteamVR mode is still the way to go if you want to use Vulkan rendering.
This is correct.
The Oculus OpenXR runtime files are already installed with the Oculus software, and AeroFly doesn’t even use OpenXR.
As for the registry key, that is just a pointer to the Oculus OpenXR files too. Note that they’re in the same folder where the rest of the Oculus software is installed.
You can create this registry key easily yourself by going to the Beta tab of the Oculus software and clicking the button that says to set Oculus as the OpenXR runtime. But again, this makes no difference for AeroFly because it doesn’t even use OpenXR.
There really is nothing special you need to do to use AeroFly with the Quest 2, except be aware that Vulkan has a bug with the native Oculus build, so if you want to use the Vulkan renderer, launch it with SteamVR as the runtime.
Lastly, the “fast” frame sync setting was a workaround for a bug that used to cause frame timing issues with Oculus Link and certain apps (XPlane and MSFS being two of them, but not AeroFly). It was finally fixed many months ago, and that setting no longer matters either, but it never mattered for AeroFly regardless.