Do note that it’s NT$ 5 million. And it can include FCY balances at a bank in Taiwan. Not US$ 5 million like some people incorrectly assume.
I think there are quite some people in a similar situation as you in the Gold Card thread who successfully converted to a APRC having only freelance income ( @Andrew ?) :
It should also work for an overseas company as long as it can pay you a salary. You can then declare this as salary in Taiwan (it counts as Taiwan-sourced as the work was performed in Taiwan).
Another option would be involving an EOR (Employer of record) solution - either through your own company abroad or directly through your customers. However, this could result in fees of US$300+ per month…
I think @Marco went that route: Started a company in Taiwan and eventually converted to APRC. It’s probably the “safest” (i.e. most straightforward) way as you will have “real” local salary. See this thread for details: