I'm experiencing a similar problem - the texture are attached when viewing the files in Xcode, but the model shows only in white. Any suggestions?

Maybe this helps some one… I'm constantly trouble shooting this issue. A couple of things that I noticed helped in a variety of situations. TRY: join all meshes into one delete the texture of the material and relink them to the material make sure all of the fils are the same bit depth and pixel size and format - 3 of the files (occlusion metallic and roughness) get assembled as one in the RGB channels so pixel size and bit depth may play a role. apply scale and rotation. re-export the file from which you generated the usdz. I usually have to export a glb and with that I'm able to generate a USDZ. (if anyone knows of a native blender usdz exporter that works let me know - the addon no longer works as of this post) applying the modifiers before exporting. These are a few things I keep an eye on. Hope this helps. If anyone has any other suggestions to this madness please share. I'm all ears.