What is the most efficient way to set the main camera to render a specific angle view at a higher resolution?

For performance purposes, I am trying to find a way to make the main camera render its entire field of view at a significantly lower resolution than a selected portion of the camera's view. For example, how would I set the camera to render a neighborhood of pixels near it's center of view ( say +/- 5 degrees in x and y) in a set resolution, while all remaining areas at only a quarter of that resolution (and upscaled).

For now, I am using multiple cameras rendering to a target textures set at different resolutions and displaying them as a RawImage on the UI. Bellow, you can see that the center of an example rendered image is much clearer than the surroundings. Although the method works, it is performance inefficient and causes low-res and high-res texture misalignments .

Thanks.