For consent to be valid under the GDPR, the controller must be able to demonstrate that the data subject agreed, and any consent request must be "presented in a manner which is clearly distinguishable from the other matters, in an intelligible and easily accessible form, using clear and plain language." Data subjects retain the right to withdraw consent at any time, and withdrawal must be as easy as giving it.
For AI training, this matters: using personal data — conversations, images, behavioral signals — without proper, revocable, clearly-presented consent fails GDPR Article 7. Buried checkboxes, bundled "agree to everything" buttons, and opt-out frameworks for high-impact processing all run into trouble here.