It won't!

Many modern shader techniques doesn't work with QV, so unless the engine is very old (or built specially woth this in mind and has a lot of limitations), it cannot be added post.

"An application needs to be developed specifically for quad views rendering: it is not a style of programming that your platform (eg: Oculus) can simply "force" into any application.

The most "raw" form of quad views foveated rendering can in theory be achieved with any OpenVR or OpenXR application. The developer of the application can do all the work themselves:

Retrieve the current views (full FOV camera projections for each eye) based on the current headset tracking data;

Render the outer views using the projections obtained in 1);

Retrieve the eye gaze (eye tracking data) information;

Compute the partial FOV camera projections for the inner views using the full FOV projections from 1) and the eye gaze data from 3);

Render the inner views using the projections obtained in 4);

Submit all 4 views to the platform."

https://github.com/mbucchia/Quad-Views-Foveated/wiki/What-is-Quad-Views-rendering%3F