The differences are defined in the Recruitment and Employment of Foreign Professionals law:
https://law.moj.gov.tw/ENG/LawClass/LawSearchContent.aspx?pcode=A0030295&norge=4
May I ask the source for where is states foreign professionals can aquire APRC after 3 years?
The below link you can find an English version of the proposed amendments (subject to change).
Article 14, “A foreign professional who has legally and continuously resided in the State for five years, or a foreign special professional who has legally and continuously resided in the State for three years, having resided for an average of more than 183 days each year, may apply to the National Immigration Agency for permanent residency if they meet the following requirements…”