i had clicked two pictures on my iphone x ....one is with most compatible format and other one is with high efficiency format . But when i transfer that images to files they both show .jpeg format...why is that happening ?

i had clicked two pictures on my iphone x ....one is with most compatible format and other one is with high efficiency format . But when i transfer that images to files they both show .jpeg format...why is that happening ? ......i did that again ...i had clicked another two images with different format but still it show jpeg for both .....could anybody tell me whats happening ??