If you apply via salary, you need to be employed by any company. Freelancing income doesn't count. You need to justify it with employment letter, and tax return.

The other way is to qualify for any of their "talent" needs. Blockchain, VR, IA, and have proof it it (publication, work, projects). They have 8 categories of people that can qualify: https://foreigntalentact.ndc.gov.tw/en/cp.aspx?n=128B875DE9C...