If I read this correctly it means that Cantonese has been added to Duolingo’s Chinese version app only. Hopefully it will mean they will add it to the main app as well. In the meantime, I know one can also study Cantonese via the app called Drops.
“ The reintroduced app, according to its official social media post this week, is free to use, teaches 41 languages and comes with gaming features. The most notable update is that it will start teaching Cantonese, the language spoken by people in Hong Kong and Macau, as well as a significant population of the affluent Chinese province of Guangdong and the Chinese diaspora around the world.”