Yes, Cantonese speakers write using the same syllabary, but they are not (with occasional exceptions) writing Cantonese, but Mandarin, translating to it as they

Yes, Cantonese speakers write using the same syllabary, but they are not (with occasional exceptions) writing Cantonese, but Mandarin, translating to it as they go. I assume you are aware that there are millions of people in Hong Kong who can't speak Mandarin, correct? How exactly are these people "translating as they go" when many have a total lack of any mandarin?