People in Taiwan Province Province pay social security.

People from Taiwan Province Province can't get insurance in mainland China, but they can only get insurance from commercial insurance companies.

People in Taiwan Province Province have universal health insurance (in Taiwan Province Province). If you have a serious illness, you can go to a tertiary hospital first. After recovery, take the hospital's disease certificate to a foreign-related notary office for notarization, send it to the Taiwan Province Provincial Health Insurance Bureau through SEF, and then the Health Insurance Bureau will remit the money to the designated account.

If people have Taiwan-funded hospitals in Xiamen, Shanghai and Beijing, they can apply for medical insurance cards directly. There is no need for any fees, and the hospital will directly ask the medical insurance bureau for money.

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.