I Googled around, and I cannot find any significant fines Facebook has faced for violating GDPR. The enforcement tracker you yourself linked (https://www.enforcementtracker.com/) only has one irrelevant entry for Facebook, and this feed (http://newsbreaks.infotoday.com/NewsBreaks/GDPR-2020-Where-C...) which was last updated just this August says litigation is pending.

If you have any sources for this fine, please post them.