Taiwan is a gorgeous and fascinating country. Just saying "where should I go?" to a bunch of internet strangers without providing any guidance on your interests is unlikely to elicit very useful responses.

For what it's worth, I went for two weeks at the end of '19, and I could easily and happily have spent an entire month - or longer - there. It's really a great place to visit. I spent a week in Taipei (which was a couple of days more than I initially planned to, but I loved the city and had jet lag my first couple of days, so I wanted some more time to explore), then went down to Taroko Gorge/Hualien and then to Tainan for a few days.