What does 餅乾 mean in Taiwan?
I am Taiwanese, and I have even had this "餅乾" once.

Generally, we can refer to almost every snack that is made with flour and "cracks" in your mouth as 餅乾. So when you say you want some 餅乾, people will not only give you crackers, but also cookies, potato chips, wafer cookies, wafer rolls, mille feuille, etc. These things have their own specific names, of course!

Even these are 餅乾: Jagabee Fries, and Pocky.

I would also like to clarify that this sentence is not in Taiwanese. It is in Standard Chinese, but we have our own accent and wording. Just like the differences between American English and British English. We normally speak two languages in everyday life, i.e. Chinese and Taiwanese, a Min dialect.