More than a year ago, I wrote an article criticizing Irish DPC's interpretation of Facebook's legal basis.
This troublesome interpretation has [fortunately] been overturned by the European Data Protection Board which found that the ‘contract’ basis was not a lawful one for processing personal data for the purpose of targeted advertising.
my article : https://verfassungsblog.de/why-are-you-on-facebook/
a good article on the EDPD's decision by @bertuzluca
https://www.euractiv.com/section/data-privacy/news/facebook-instagrams-legal-basis-for-personalised-ads-found-in-breach-of-eu-law/