Heppner's argument was dumb but it opens a field of interesting questions. If I use a document processor (like Google Docs) to compose a message to my attorney, which message itself would be privileged, but I use some sidebar feature of Google Docs/Gemini to clean up a sentence that I thought was clunky, and elsewhere I have, for whatever reason, enabled features that permit Google to use inputs and outputs to train or refine their models, has that destroyed the privilege?
Yes, you lose the privilege if your attorney-client communications are not intended to be confidential. If you agree to share those communications with a third party, you don't intend them to be confidential.
What about email?
The brief linked above[0] was easy to read. IANAL but in it the author seems to say that online tools fail to meet the confidentiality "test" and explains the ruling in clear language.
[0] https://news.ycombinator.com/item?id=47779377