Most profitable (non Taiwanese) bank in Taiwan is

Taiwan Living in Taiwan
1

https://www.facebook.com/cbc.gov.tw/photos/a.1991441454273428/3888628344554720/?type=3&theater

Central Having some humor in the posting (style) using baseball as a backdrop

Anyways the most profitable are:

獲利前3名依序為日商瑞穗、美商摩根大通及法商法國巴黎銀行在臺分行。 In english : Mizuho Bank/MHFG ,JP Morgan Chase , BNP Paribas ( Banque Nationale de Paris)

notes: Mizuho Bank/MHFG is 4th largest Japanese bank but big in Taiwan. BNP Paribas is interesting but it is the biggest in the EU and active in the Western USA. In General they serve business or large customers so most here do not notice them like Citi Bank which has retail branches.

2

JP Morgan and BNP Paribas likely getting their profits from their securities branches.
You must separate the IBs from the commercial banks.