As I understand the only way an American, or any foreigner for that matter can enter Taiwan now as of November 23, 2020, is if they’re hired from abroad and sent a work permit. Then they would need to provide a negative covid test result.
The best way for a lot of Americans starting out in their careers would be to get a teaching job. Some companies like Hess or public schools may be quite desperate for foreign English teachers and will go through the process to send a work permit to the United States to get the new teacher over to Taiwan. Unfortunately this is much more of a hassle than just arriving on a landing visa.