There is no way to make a true isometric view of a 3d scene in After Effects because there is no isometric camera in After Effects. If you need true isometric, you either need to use a different program that does have an isometric camera, or animate in 2d.
That said, you can approximate isometric, by putting your camera really far away from your scene, and setting the zoom level on the camera really high. This minimizes the perspective in the scene, but you won’t get rid of perspective entirely. It will also make camera moves tricky. If you need camera moves, you are probably best off keeping the camera in place, and moving/rotating the scene.
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