Having the same problem and my code looks virtually identical to yours. In the logs I see the following error:
[ShareSheet] Couldn't load file URL for Collaboration Item Provider:<NSItemProvider: 0x600003f86840> {types = (
"public.comma-separated-values-text"
)} : (null)
Wish that the catalog app in the talk was available in the samples so I could test that and compare to what I have.