While no it cant force it for free and they are free to have an Ad based version the cookies could be considered a violation of the ePrivacy regulation:

Allow users to access your service even if they refuse to allow the use of certain cookies

Make it as easy for users to withdraw their consent as it was for them to give their consent in the first place.

Although the EU has been pretty lax in terms of enforcing a lot of these regulations

Most likely ePrivacy rather than GDPR although in most discussions they become the same thing

Its sad how relatable this is