Another possibility in fanfiction is that Naruto succumbs to a deadly disease or poison. It could be a new, mysterious illness that the medical ninjas in the village can't cure in time, leading to his death.
Well, as of now, Naruto is still alive in the Boruto manga. There might be some intense battles and challenges, but no death for him yet. Maybe you got some wrong information?
There could be a scenario where Naruto sacrifices himself to save Boruto or the entire Hidden Leaf Village from a catastrophic event like a massive attack by an unknown and dangerous force. He might use all his chakra to protect the village, leaving him with no energy to survive.