Adding iPhone 12 Pro Max to Chromes Emulated Devices

In Google Chrome Inspector (Developer Tools) Click on edit then Add custom device

iPhone 12 Pro Max
428 x 926 x 3
User agent string =
Mozilla/5.0 (iPhone; CPU iPhone OS 13_2 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.0.3 Mobile/15E148 Safari/604.1
Mobile

That’s all you need.

Here is some additional info for iPhone 12 Pro Max:
Display: 6.7″ Super Retina XDR (OLED)
Screen resolution (points): 428 x 926
Native resolution (pixels): 1284 x 2778 (458 ppi)
Scale factor: 3x
Portrait size classes: w: Compact, h: Regular
Landscape size classes: w: Regular, h: Compact

Hope this helps
Regards, James