with Taiwanese Mandarin I mean 臺灣國語, also called 華語.
All I find online, given how relevant China is today is the simplified script and PRC vocabulary, not the vocabulary used in Taiwan.
Even translators advertised as offering Taiwanese Mandarin translate into Chinese Mandarin.
Not exactly what you asked for but OpenCC.
Taiwanese Mandarin has a history no longer than eighty years. Taiwan did not have such a language until old scholars who grew up in Peking fled there and thus taking their dialect with them. China formalised pretty much the same dialect as Mandarin later. This is the super watered down version of it’s history and please resesrch yourself if you want to know more.
If you consider it to be vastly different from Mainland China Mandarin and insist to learn “Taiwanese vocabulary” I would say you’re picking bones from an egg.