iPhone 13 Pro.Night mode not working

I am using an iPhone 13 Pro. I have noticed that the Night Mode on the native camera app is not working. Ideally, the image has to be captured at the manually selected exposure time(shutter speed).But the final image, after processing, shows a random exposure time(short exposure).I contact apple chat support and visited an authorized service centre too. But nobody seems to have any clue about the issue. Please refer to the image- the time for which the image was captured was 5 seconds) . Am I doing something wrong here? Please help!