Follow these steps:

• Jump to the site hotspot3d.com. That will show you the current default, comparing the iPhone XS and the iPhone XS Max. Tap and drag to rotate the rendered images. Be sure to go left/right and up/down.
• Once you’re done playing, tap the “Apple iPhone XS” label (upper left corner), then tap the iPhone 8 Plus. You should then return to the main screen, with the iPhone XS Max and iPhone 8 Plus, side-by-side. Rotate as you like.

This is an interesting tool, but it makes a specific point. The iPhone 8 Plus and the iPhone XS Max are almost identical in size (the Max is actually just a smidge smaller), but the Max has a much, much larger screen, even taking the notch into account.

Enjoy.