https://wccftech.com/iphone-12-pro-max-design-leaks-looks-similar-to-ipad-pro-video/

As per the newest leaks, courtesy of EverythingApplePro, iPhone 12 Pro Max Design is all but confirmed to look like a mini iPad Pro. It has a flat design, with curved edges, flat non-curved glass, smaller bezels, and a smaller notch.

EverythingApplePro got their hands on an iPhone 12 Pro Max CAD file via Max Weinbach, which they used to 3D print a dummy model. This CAD file is usually provided to accessory manufacturers in advance so that they can work on their products.