But that communication is clearly intended to be confidential. Also isn't having one attorney on a multi-party communication marked confidential sufficient to create privilege?

That is an erosion of the social contract from the early days of SaaS.

The law in the US is based on the expectation of privacy. If companies and the US government repeatedly egregiously share private data in violation of terms of service and the law, then what expectation is there?

25 years ago, I'd say "Checking the 'do not train on my data' button in an Anthropic account would pretty clearly create an expectation of privacy." These days? OpenAI had to send all such data to the New York Times, the government has been illegally wiretapping the whole planet for decades, the US CLOUD Act exists, and companies retroactively change terms of service all the time.

Heck, Meta has been secretly capturing lewd bedroom videos and paying people to watch them, and it barely made the news, just like the allegations the WhatsApp content moderation team made where they claimed they have access to WhatsApp E2EE content (what other content could they be moderating?!?)

What constitutes "Sharing with a third party" though? Using a 3rd party email service like outlook or gmail? Using a third party docs service like google docs?

It doesn't seem right that google docs would be privileged, but if you use the fancy spellcheck button, it no longer is.

Right so calling my attorney is the same since I'm sharing the call with the phone company.

I don't think that hot take will survive much contact with the near future, at least not without a good deal of controversy.