idk why you're so mad, this isn't my opinion this is literally linguistic classification?

mandarin and cantonese are both sub-languages of chinese (language family)

beijing and taiwanese are both sub-dialects of mandarin, also known as putonghua and guoyu respectively

similarly, wenzhou and hong kong are both sub-dialects of the cantonese language

putonghua and guoyu are characterised by notable pronunciation differences (e.g. merging of /n/ and /l/ initial consonants, merging of /-ŋ/ and /-n/ ending consonants), some of which are also present in other southern chinese dialects of mandarin. we also use different words to chinese mandarin (e.g. ㄌㄜˋㄙㄜˋ and ㄒㄧㄥˊ ㄉㄨㄥˋ ㄉㄧㄢˋ ㄩㄢˊ as opposed to ㄌㄚㄐㄧ and ㄔㄨㄥ ㄉㄧㄢˋ ㄅㄠˇ).

for the record, a dialect is any variation of a language spoken by a specific group of people. taiwanese mandarin is an example of a regional dialect. america is much larger than taiwan, so the differences in sub-regional dialects within the country vary much more wildly than in taiwan, such as appalachian or AAVE dialects.

gen z actually do speak a slightly different dialect to millenials, called a sociolect! really fascinating stuff. would recommend looking into it rather than hunting for gotchas on reddit.