Perhaps he realizes that the fanfiction is taking him in a direction that doesn't align with his true character. Harry is known for his integrity, and if the fanfiction was making him act out of character, he might give up.
Fred and George Weasley are beloved in fanfiction. In the context of the Goblet of Fire, they could be involved in some wild schemes related to the tournament, like creating their own magical items to help Harry or just causing general chaos and hilarity around the events of the Triwizard Tournament.
One interesting plot could be an alternate version of the Triwizard Tournament where the tasks are even more dangerous and magical creatures from other regions are involved. For example, instead of just a Hungarian Horntail, there could be a whole nest of them to face in the first task.
It might imply that within the context of a Goblet of Fire - themed fanfiction, Harry Potter reaches a point where he can no longer continue. He could be tired of the events, or perhaps he realizes that the path he was on in the fanfiction was wrong. For example, if the fanfiction had him in a dangerous situation in the Triwizard Tournament that was getting out of hand, he might choose to give up to protect himself or others.
In many of these fanfictions, Norbert's relationship with Hagrid is often explored further. For example, in some, Norbert misses Hagrid deeply after being sent away. Another interesting plot point can be Norbert's impact on the magical environment around Hogwarts. Since he's a dragon, his presence can cause all sorts of magical disruptions.
One great 'Harry Potter Norbert GOF fanfiction' is 'Norbert's New Adventure'. It explores what could have happened to Norbert after he was sent away in 'The Goblet of Fire'. Another interesting one is 'Norbert and the Forbidden Forest', which delves into Norbert's possible interactions within the Forbidden Forest.
One idea could be exploring what would happen if a new, mysterious student joined Hogwarts during the Triwizard Tournament. This student could have a hidden agenda related to the Dark Arts and start influencing the events of the tournament in unexpected ways.
Hermione Granger is also very popular. In fanfiction, she might be given more complex storylines, such as her own investigations into the strange happenings around the Triwizard Tournament that go beyond what was shown in the original book.
Some fanfictions might focus on different relationships. Maybe a story where Harry forms a closer bond with Cedric Diggory before the tournament, changing the dynamics of the events. It could show how they might have worked together more or influenced each other's strategies.
Winky the house - elf. She has a lot of potential. In a fanfic, we could explore her life after being freed from the Crouch family. Maybe she has some unique knowledge about the Dark Arts or the Triwizard Tournament that she's been hiding. Her loyalty and her struggle with her new - found freedom could be really interesting to write about.