Citation? I think this is not true. The EU law seems to just require explicit consent. So websites and apps can ask whether user wants to share data to keep using them for free or pay a subscription fee.
Article 7 https://gdpr-info.eu/art-7-gdpr/
Recital 43 https://gdpr-info.eu/recitals/no-43/
Those two in combination stop companies processing data for unrelated task to the services they provide. And it's indeed true and already been applied, see this: https://www.digitalguardian.com/blog/google-fined-57m-data-p...
[0]: https://en.wikipedia.org/wiki/Consent_or_pay [1]: https://uoou.gov.cz/urad/povinne-zverejnovane-informace/svob...