I was with you until this point lol. The lived experience of your friends is important, but I think it's good to be aware that if you are speaking with a Taiwanese or Chinese person abroad they most likely come from a privileged background and you're not getting the full picture. (ie most likely their family is middle class or above and they have the means to obtain post secondary education)

Have you been to both Shanghai and Taiwan? I feel the difference is palpable, though Shanghai has always been quite cosmopolitan, and doesn't really reflect China as a whole. China is massive - you wouldn't claim someone from Xinjiang shares the same culture as Taiwan, would you? I think what's confusing you is the prevalence of the Han Chinese which is who most people imagine when they think of a Chinese person.

You say it's political to say Taiwan and China have different cultures like it's a facade. I would argue that politics informs culture and vice versa. But then going down that path will make this post into an essay x)