Dutch colonial rule began in 1642, so Taiwan will have been a Dutch colony for over 300 yesrs. Expect dramatic cultural changes compared with OTL.
I imagine an outline of the history of Taiwan might go something like this:
Dutch control of the island is solidified by the 1700s- ish. The Qing Dynasty will eventually drop their territorial claim to Taiwan.
(White) Dutch people start colonization of the island, maybe in the more hospitable (by European standards) north. I can't imagine there being any actual slavery of native Taiwanese people, but they will definitely be poorer and seen as inferior by Europeans.
Dutch is the language of administration. The lack of a common language for the indigenous people leads to Dutch being used as a lingua franca. Over the next few hundred years (1700-1900), as the Dutch retain firm control of the island and knowledge of the Dutch language is necessary, indigenous languages slowly die out. Comparable situations: Brazil, Mexico?
After World War 2, the Republic of China obviously won't be able to flee to Taiwan as in OTL. They'll probably flee to Hainan instead, with TTL Hainan serving a similar role as OTL Taiwan.
By the time of independence in the 1970s, Taiwan has maybe 10% of its population genetically European, 20% mixed-race, and 70% native Chinese/Taiwanese. The native people had been oppressed for most of the duration of colonial rule, but this situation started to improve post-WW2.
The shared experience of surviving Japanese occupation during WW2 may contribute towards the development of a Taiwanese national identity for everyone regardless of ethnicity.
Taiwan today will be a developed country, and retain a close friendship with the Netherlands.