The Microsoft Flight Simulator 2024 beta now has fixed foveated rendering, and the sim will get eye-tracked foveated rendering support in the future.
The beta channel of the simulator has a Foveated Rendering toggle in the VR settings, with the following description:
When active, uses quad views rendering technique to improve your GPU performance. The the higher resolution, the higher the gain. Can add some CPU overhead. Can be combined with Eye-Tracking when available for best use.
The toggle isn't mentioned anywhere in the beta changelog, but testing it I can confirm that it currently activates fixed foveated rendering on any VR headset, netting a 5-10 FPS performance improvement, with the tradeoff of some pixelation at the edges of my view.
However, eye-tracked foveated rendering doesn't yet appear to be working, suggesting that it will be added at a later point in the beta cycle. I confirmed this by testing with a Quest Pro, and VR Flight Sim Guy also found the same with a Pimax Crystal headset with eye tracking.
When it does arrive, eye-tracked foveated rendering could bring significantly greater performance gains for headsets with eye tracking, on the order of dozens of frames per second.