Dumbledore, as Harry's guardian in the fanfiction, would probably use his influence in the wizarding world. He could make sure that Harry is taught by the best teachers at Hogwarts. He'd also be there to offer advice and guidance, especially when Harry faces challenges like dealing with Voldemort or other dark forces. For example, he might teach Harry some advanced defensive magic privately to better protect himself.
One reason could be that Dumbledore had too many other responsibilities in the wizarding world. He was the headmaster of Hogwarts and was constantly involved in dealing with the threat of Voldemort on a larger scale. He might not have been able to give Harry the individual attention and care that a true guardian should provide.
One possible reason could be that Dumbledore wants Harry to have a more normal upbringing away from the spotlight of Hogwarts and his own influence. So he deliberately steps back from the role of guardian.
Perhaps Sirius Black could be Harry's magical guardian instead. In the original story, Sirius had a strong connection to Harry and a great desire to protect him. Even though Dumbledore was a major figure in Harry's life, Sirius was his godfather and had a natural claim to the role of guardian.
Harry might initially be confused. He has always looked up to Dumbledore, so when he realizes Dumbledore is trying to control him, he could start to question everything he thought he knew about their relationship. He may become more rebellious as a result, trying to break free from Dumbledore's influence and make his own decisions.
It might make Harry more confident. With Dumbledore's training, Harry gains more knowledge and skills, which gives him the confidence to face challenges.
In some fanfictions, Harry might be depicted as Dumbledore's pet in a metaphorical sense. It could be that Dumbledore is overly protective or manipulative in the story, making Harry seem like a 'pet' under his control. But this is not a common or canonical view, just a creative interpretation in certain fan - created works.
There probably is. Fanfiction is a place for fans to re - imagine the stories they love. With Dumbledore as Harry's grandfather, it could mean that Dumbledore had a more personal stake in Harry's well - being from the start. It might also lead to different backstories for Dumbledore himself, like how his family ties to Harry came to be. It could even change the way the final battle against Voldemort plays out, as Dumbledore's family connection to Harry could bring in new elements of strategy or sacrifice.