When I got to Taiwan, moonies were flourishing. After them, light of the day or something like that. Seems like in some different incarnations, the same evil never dies.
Do foreigner religious leaders need a work permit guessing they already have a visa.
Missionaries need work permits, unless they’re exempt through marriage etc.
But a “religious leader”? I suppose it depends on what the position involves.
They can get a missionary visa, but only if sponsored by a recognized local religion or organization. There are other conditions, e.g. for salary / financial support.
A decade or so ago, I recall reading about foreigners who managed to get missionary visas based on ministerial credentials issued by the (US-based) Universal Life Church. In case you’re not familiar with the ULC, it grants such credentials to anyone who asks (no money, no required beliefs, just fill in a short form on their website), and has won their recognition in various US states, e.g. to perform weddings. (If you want your friend to perform your wedding, this is the easiest way to get them a license to do so.)