Thanks for posting here too. From the discussion at Hacker News it doesn't appear to be as bad as the headline suggests though. I'll copy the comment that makes me say that here in case people don't follow the link:
minimaxir 1 hour ago | next [–]
Title is misleading given what the help article linked says: https://help.dropbox.com/view-edit/privacy-settings-dropbox-ai
What information is shared with third-party partners?
Your files within Dropbox are sent to a third-party AI only when you chose to interact with AI powered features. For example, when you ask a question about a file.
At this time, we’re partnered with one third-party AI partner, OpenAI. Open AI is an artificial intelligence research organization that develops cutting-edge language models and advanced AI technologies. Your data is never used to train their internal models, and is deleted from OpenAI’s servers within 30 days.