The CNIL is responsible for interpreting the law in France. That some of Google's settings did not, in its view, comply with the laws in place concerning the RGPD. Google's data analysis platform is not, strictly speaking, illegal... at least for the moment.
Nevertheless, if your site uses Google Analytics, you risk being pinned for transferring personal data out of the E.U., and you'll have 30 days to opt out.
The penalty can amount to up to 4% of your sales.