Well, it depends on the fanfiction. Some fanfiction writers choose to make Naruto unbeatable to show his ultimate growth and development. They might give him new powers or make his existing ones so overpowered that no one can stand against him. But not all fanfictions follow this pattern. There are also those that explore Naruto's vulnerability and his struggles, which makes the story more complex and realistic in a way. For example, there could be fanfictions where Naruto has to face enemies that can exploit his emotional weaknesses, even if he is physically strong.
Yes, in some fanfictions Naruto is unbeatable. These fanfictions usually focus on highlighting Naruto's already strong traits like his determination, his large chakra reserve, and his never - give - up attitude. By making him unbeatable, the authors can create a sense of pure admiration for the character. But of course, this is just one type of fanfiction among many, and there are also those that take a more balanced or even a 'weak - Naruto' approach.