Meta have emailed saying they have a "legal basis called legitimate interests for using your information to develop and improve AI"
They provide a link to a form to object to this processing:
https://www.facebook.com/help/contact/6359191084165019
It asks the these two questions:
Please tell us how this processing impacts you. (Required)
Please provide any additional information that could help us review your objection. (Optional)
On what grounds can I object?