Meta said in a blog post that its Advanced Chat Privacy is a toggle setting that opts chats out of AI features and also keeps chats from being downloadable or from making media auto-downloadable to devices. The blog post does not specifically mention Meta AI. The blog post reads in part:

WhatsApp is adding a new privacy feature that blocks people from exporting the contents of a chat. Called Advanced Chat Privacy, the feature is available with the latest version of the app. You can enable it for both individual and group chats by tapping the chat name and turning on Advanced Chat Privacy.