Fakebook messaged me and suggested I could object to their collection of data for Meta AI, so I did. The reply:

We will honour your objection for your public information, such as public posts and comments. This means that we won't use your public information from Facebook and Instagram for future development and improvement of generative AI models for our AI at Meta features and experiences.

Do we believe them?

note the spelling of honour - they know I live in the UK cf US (or possibly Oz/NZ/SA etc) - so much for their honour!