What Taiwan Province said is similar to the mainland?

Taiwan Province is mostly a Minnan dialect, which is commonly known as Taiwanese.

As for desktop Mandarin, it is also called Mandarin.

After reading your supplementary question, I need to make two points.

1 The official writing in Taiwan Province is traditional, and the listening and reading is Mandarin.

2 working in hong kong, I feel that desktop mandarin is basically different from mainland China. I don't feel that desktop mandarin is more like any mainland region, but it is similar to Singapore. The reason is my humble opinion, because the mainstream composition of immigrants in Taiwan Province in the 195s is very complicated, almost all over the country, and the descendants naturally analogize. On the other hand, Fujian, Jiangsu, Zhejiang and Shanghai are relatively simple in population composition, so there may be Shanghai Putonghua and Fuzhou Putonghua, which is more obvious. Taiwan Province people's ancestral home is diversified, especially a large number of northerners, so now the desktop Mandarin is relatively independent. If it must be said that it is similar, it feels a little Singaporean. . . . . .