USDZ is the format that Apple is backing for VR/AR delivery (developed by Pixar)[1]. We're betting that it is what is going to be used in any Apple headset.
Right now you can't easily view USDZs in the browser (the format is a moving target), however Apple is making strides to make it available with the proposed Model element[2].
We were doing some USDZ --> GLTF converstion (GLTF being a format that will work in the browser), but it is jankey (technical term).
I have not tried an iPhone 6 yet. I will have to pry it from my children's hands and remove a layer of cheese and excretions before I do.
I've made a video on how to do this via the browser here[3].
TBH, the experience a heap better in the iOS App (currently in testflight) [4].
[1] https://graphics.pixar.com/usd/release/wp_usdz.html (seem to have cert issues) [2] https://github.com/WebKit/explainers/tree/main/model [3] https://usdz.app/screencasts/getting-started [4] https://testflight.apple.com/join/VteIxFd7
It would be nice to have some idea going in for what the requirements are. - I have to admit, I don't understand why I can't preview the 3D experiences right on my computer. - Likewise, when I try the QR code on my iPhone 6 ... well, I'm hardly surprised to not see anything in 3D, but it wouldn't hurt to have a little more detail than "Scan this QR code on your iPhone or iPad."
I suppose I could mention that I've done some game development and a little bit of VR/AR, but have never heard of the USDZ file format before.