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.

There are websites that can swap between simplified and traditional Chinese characters

in my experience learning characters I needed to learn how to write them, starting from basic strokes - there are some good videos on youtube, you have to be patient, this takes a long time

for traditional characters and Taiwan dialect you'd want to learn bopomofo and not pinyin, for the reasons other people raised. From what I have seen bopomofo would also help learning the basic strokes and some radicals

i found a podcast called Dimsum Pinyin really really helpful for training my ears to tones, and pinyin in general, but there are likely better resources from ROC. There's probably a lot out of ROC, if you look for 'comprehensible input' videos itll help.

hanping dictionary app and pleco dictionary were really helpful when i started, they both have paid features showing stroke order for characters

Ive seen people say you dont need to learn hanzi, but it's not only fun, it's really helped me remember words. If I hear a phrase and can identify the characters, it's much easier to remember what it means. the character for cat, 猫 mao, is a radical for dog 犭quan, grass 艹 cao, and field 田 tian

anyway, rambling while i procrastinate, good luck

You wouldn't be using pinyin for this.

Pinyin is specifically tailored for the Beijing dialect (which is now what you call mandarin) back in the 1950s. Other dialects or regional variants do not translate well into pinyin.

For example, Shanghainese and all Wu-style dialects have 5 tones instead of 4. If you're using Pinyin you're using the Beijing pronunciation.

Pleco is the dictionary app I use. It does a good job translating phrases I type in and supports a variety of input methods. It has traditional Chinese characters as an option and offers the zhuyin(bopomofo) display as an option too.

That's interesting because I usually have the opposite problem.

The more complex characters are generally called "Traditional Chinese" in English if that helps