usdz-export-addon.py

import bpy
from bpy_extras.io_utils import ExportHelper
import os
import sys
import shutil
import struct
import tempfile
import zipfile

bl_info = {
    "name": 'USDZ export',
    "category": 'Export',
    "version": (1, 0, 8),
    "blender": (3, 0, 0),
    'location': 'File > Export > USDZ',
    'description': 'Addon export USDZ models.',
    'tracker_url': 'https://github.com/floorplanner/fp.blender.render/issues/',  # Replace with your issue tracker
    'isDraft': False,
    'developer': 'Tim Knip',
    'url': 'https://github.com/floorplanner/fp.blender.render',
}

def usdzip(output_filename, source_dir, verbose=False):
    """ zip files with 64 byte alignment
        see: https://github.com/101arrowz/fflate/issues/39#issuecomment-777263109
    """
    offset = 0
    with zipfile.ZipFile(output_filename, "w", zipfile.ZIP_STORED) as zip:
        relroot = os.path.abspath(
            os.path.join(source_dir, os.pardir, os.path.basename(source_dir)))
        for root, dirs, files in os.walk(source_dir):
            for file in files:
                filename = os.path.join(root, file)
                if os.path.isfile(filename): # regular files only
                    info = zipfile.ZipInfo.from_file(filename)
                    arcname = os.path.join(
                        os.path.relpath(root, relroot), file).replace('\\', '/')
                    info.filename = arcname
                    if verbose:
                        print('adding %s' % arcname)
                    header_size = 34 + len(arcname)
                    offset += header_size;
                    offset_mod64 = offset & 63
                    if offset_mod64 != 4:
                        pad_length = 64 - offset_mod64
                        info.extra = struct.pack(
                            'hh%ds' % pad_length,
                            12345,
                            pad_length,
                            b' ' * pad_length)
                    with open(filename, 'rb') as f:
                        data = f.read()
                        zip.writestr(info, data)
                        offset = len(data)

def export_usdz(outfile):
    print('saving model as %s' % outfile)
    tmp = tempfile.mkdtemp()
    basename = os.path.basename(outfile)[:-5]
    out_usdc = os.path.join(tmp, '%s.usdc' % basename)
    print('exporting tmp file %s' % out_usdc)
    try:
        if not os.path.exists(tmp):
            os.makedirs(tmp)
        bpy.ops.wm.usd_export(
            filepath=out_usdc,
            generate_preview_surface=True)
        usdzip(outfile, tmp, True)
    except Exception as e:
        print(e)
    shutil.rmtree(tmp)

class OpenFileBrowserOperator(bpy.types.Operator, ExportHelper):
    """Export current scene to USDZ"""
    bl_label = "Export file"
    bl_idname = "usdz.filebrowser"

    filter_glob: bpy.props.StringProperty(
        default='*.usdz',
        options={'HIDDEN'}
    )

    filename_ext: bpy.props.StringProperty(
        default='.usdz',
        options={'HIDDEN'}
    )

    check_existing: bpy.props.BoolProperty(
        name="Check Existing",
        description="Check and warn on overwriting existing files",
        default=True,
        options={'HIDDEN'},
    )

    def execute(self, context):
        export_usdz(self.filepath)
        return {'FINISHED'}

def menu_func(self, context):
    self.layout.operator(OpenFileBrowserOperator.bl_idname, text="Universal Scene Description (.usdz)")

def register():
    bpy.utils.register_class(OpenFileBrowserOperator)
    bpy.types.TOPBAR_MT_file_export.append(menu_func)

def unregister():
    bpy.utils.unregister_class(OpenFileBrowserOperator)
    bpy.types.TOPBAR_MT_file_export.remove(menu_func)

if __name__ == "__main__":
    register()

In Blender 3.0 and higher:

1. Edit > Preferences > Add-ons
2. Install > browse to usdz-ezport.addon.py and check the checkbox

There will be a new entry under File > Export > Universal Scene Description (.usdz)

The addon uses the existing export to USDC and zips the created directory following the specs for the zip file