model-viewer: Transparent background doesn't work in ar in iphone and ipad

Description

Transparent background doesn’t work in ar in iphone and ipad,

Live Demo

https://modelviewer.dev/examples/augmentedreality/#transparentBackground

open in iphone or ipad click ar button, all transparent part are black

if you upload a glb model contain transparent material to https://spase.io/playground convert to usdz model,then use html code <a href="./your.usdz" rel="ar"> <img src="your.png" alt="" width="250" height="250"> </a> ar transparent will work fine in iphone

Version

• model-viewer: v1.7.2

Browser Affected

• Safari

OS

• iOS 14.6

AR

• WebXR