Infrared cameras don’t really work with which animal?

Yes, polar bears are nearly invisible to infrared cameras:

Thick fur and fat: Polar bears have a thick layer of fat and fur that insulates them and prevents heat from escaping. This means that infrared cameras, which detect heat lost as infrared radiation, can't pick up a polar bear's heat signature.

Hollow fur: Polar bear fur is also hollow, similar to the fur of pronghorn antelopes.

Blended in with surroundings: Polar bears can also blend in with their snowy surroundings, making them difficult to see with visible photography.

Scientists have used this knowledge to develop "invisibility cloaks".