I wonder how many Cantonese speakers (either native or L2 learners) who don't speak Mandarin exist in the world. At least in mainland China, as far as I know almost all people born in 1980 or later have no problem in speaking Mandarin, but not sure about middle-aged people or elderly, specifically in the region where Cantonese is spoken.
There are likely many people in Hong Kong and Macau that don't speak Mandarin, but both regions don't have that large population.
I'm not sure about people outside of China, but I know there are many immigrants in the West that originally came from Hong Kong.
So I wonder approximately how many people speak Cantonese yet don't speak Mandarin.