From the project website: https://www.eea.europa.eu/en/datahub/datahubitem-view/1c1ffad2-34c3-471b-bd69-dd013cdd7b80

The monitoring of the real-world emissions from new cars and vans is based on Article 12 of Regulation (EU) 2019/631. It aims to ensure that the CO₂ emissions of vehicles determined during laboratory testing remain representative of real-world emissions of vehicles in circulation.

Real-world for new cars and vans is public available both as raw and aggregated data in csv-format.