I've not used night mode for awhile on my s21 ultra until today i tried to use it but its not processing the photos.
I googled up and tried clearing data on camera app also restarted phone but its all the same i try to change from auto to max on how long it would take to take a picture but it always stays on 1 second.
As a process of elimination try > Clear Cache Files from the phone's System Partition Section > https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/ You may need to insert your earphones or hook upto a powered On Laptop to access the Clear Partition Section. This may help with lag or stutters as this clears the phone of old/unused or broken cache files.There is also a Repair Apps option in the Menu System too.
If no joy then send the feedback via your Samsung Members App under the GetHelp section.
Also a Samsung Service Centre or Experience Store maybe able to help @Mimo40