They are referring to the message on the front page of the website.
THE DEVELOPER DOES NOT RECOMMEND TO INSTALL/USE OPENXR TOOLKIT, AS IT IS KNOWN TO CAUSE ISSUES WITH MANY OF THE NEWER GAMES RELEASED IN SINCE 2024.
My recommendation is indeed to not use it anymore. There are some known bugs that were never fixed and that never will be.
Support for DX12 was there but never finished. Injecting features with DX12 is significantly more complex than with DX11. There are several known memory leaks and other bugs with OpenXR Toolkit DX12.
Things like foveated rendering require game-specific heuristics that might not work with FS2024 or with certain settings. A good way to visualize is to look at the Toolkit’s developer overlay, things ‘VRS RTV’ are indicative of whether foveated rendering is working as expected. Low value (under 10) means bad (even if you see pixelation in periphery), a normal execution on FS2020 was something like 40+ IIRC. This showed that the renderpass heuristic worked fine. Values in between are likely subpar as well, showing that the heuristic doesn’t fully work and therefore some performance gains are left out.
This is the reason why these features need to be implemented inside the game, not outside.
Overall from reading the above, it looks like we are now entering year 4 of “subpar VR in MSFS” and the gaming industry keep showing that it doesn’t care about PCVR 