Is ContentAI accountable as per GDPR?

Sandra Wachter's post  - "Towards accountable AI in Europe" mentions the following -

AI based systems are often opaque ‘black boxes’ and are difficult to scrutinize. As increasingly more of our economic, social and civic interactions – from credit markets and health insurance applications, to recruitment and criminal justice systems – are carried out by algorithms, concerns have been raised about the lack of transparency behind the technology, which leaves individuals with little understanding of how decisions are made about them.

ContentAI uses machine learning, as per Marketo - and we have an option to choose what content gets recommended. As far as we know, once enabled, it will auto-recommend content on Emails, or Pages. Do we have control to define that? If there's a piece where Marketo recommends the same, would that be considered as compliant? Are we required to have the explanation on why did we recommended the additional content at all?