Correct you can’t process personal data based on it. And the underlying implication is that none of the consent you’ve obtained via a cookie wall is valid because you haven’t given any users the opportunity to “refuse without detriment” (because their options are to consent or see nothing). So the information you’re processing on behalf of users who clicked “I agree” - even the users who do in fact knowingly and willingly agree to the information processing - might be lacking a legal basis.