That's very different from the martial law that was effectively imposed in China. If you don't follow the law in most countries you will subject to sanctions, it's no different in Singapore. Typhoid Mary was subjected to forcible quarantine in the US https://en.wikipedia.org/wiki/Mary_Mallon

It’s just that the sanction in Singapore are much more harsh than in the West. When I visited I noticed that fines are about 10 times higher than in Canada for the same offense. And there is no caning as well.

that's a fascinating historical case, first time I learned of it. Do we know how exactly Mary spread the disease? Was it unwashed hands or saliva or her breath? How is typhoid transmitted exactly?

She was a cook who did not wash her hands thoroughly after defecating. Salmonella typhi bacteria causes typhoid and is excreted in feces. She transferred it into cold food--e.g. salads, peach ice cream--that she prepared (cooking kills the bacteria). The doctors of the time theorized that the Salmonella typhi had colonized her gallbladder. There were many asymptomatic carriers detected at the time but few if any persisted as cooks or preparing food once they had been warned.

Seems to me like a prison sentence when this blows over is reasonable for somebody violating a quarantine order without a good excuse. It's not outside of the legal traditions of the U.S. to have strong quarantine orders, nor is it particularly authoritarian.