Polar bears are carnivores and prey on many arctic birds and fish. However, under natural conditions, no one found polar bears predating any penguin. This is because

Polar bears and penguins never coexist in the wild due to their distinct geographical distributions. Polar bears are native to the Arctic region in the Northern Hemisphere, where they hunt seals and other marine mammals [t1, t5]. In contrast, penguins are found exclusively in the Southern Hemisphere, primarily in Antarctica and sub-Antarctic islands [c2, t5]. This geographical separation is so absolute that the two species are often described as "polar opposites". While polar bears are apex land predators in the North, Antarctica lacks large terrestrial predators, allowing penguins to evolve as flightless birds that nest on the ground [t2, t3]. Because they inhabit opposite ends of the Earth, there is no natural opportunity for predation to occur [t1, t6].

Sources

1. [1] https://www.nationalgeographic.com/animals/article/arctic-antarctica-wildlife-myths-explained
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 30: Climatic Regions > Natural Vegetation > p. 472