Stereopix.net is a web platform for stereographers to share their stereoscopic (3D) photographs.
The left and right part of the images are displayed on a plane, each one being on its own appropriate layer. This makes the image different for each eye in the WebXR environment, which creates the 3D effect (provided that the authors published correct images). For non-XR modes, the camera is placed in front of these planes and the focal length is adjusted to match the display area (and the render call does the right processing to show the scene appropriately).
By the way, the library to show the scene in different modes works with regular threejs scene, so I could share it here if you are interested.