Lightroom 7.0 produces "corrupted" AVIF files
The Oct 2023 update of Lightroom CC claims to support exporting to AVIF.
That's great! But the files produced are not usable by any applications outside of Adobe Photoshop.
It does not work in Firefox, Windows Photo Viewer. Firefox has had full support for AVIF for years. What's wrong with the AVIF file that Lightroom produces?
Firefox shows the following error screen:

Windows Photo Viewer shows the following:

Attached is the offending AVIF file. No HDR, quality 100%, Display P3 color space.
....
Your own web forum doesn't allow me to upload avif files. Please, try and export an avif file on your own.
Here is an attempt to upload the offending avif file to my organisation's onedrive, you might need to open in a private browsing window.
