Yes, in some fanfiction, Harry Potter is considered a Horcrux. This concept adds an interesting twist to the original story, exploring different aspects of magic and the connection between Harry and Voldemort.
One consequence could be that his connection to Voldemort becomes even stronger. This might lead to him being able to sense Voldemort's actions and thoughts more clearly, but also make him more vulnerable to Voldemort's attacks on his mind. Since the Horcrux is a part of Voldemort's soul, it could also start to influence Harry's personality, making him more aggressive or moody at times.
If Harry were to create a Horcrux in fanfiction, it would likely lead to a great corruption of his soul. Horcruxes are dark magic, and the act goes against all that Harry stands for in the original series. He might start to show signs of increased aggression, a detachment from his friends, and a growing attraction to the Dark Arts.
Well, in some fanfictions, a Horcrux might be purified through powerful magic spells that are specifically created for the purpose. For example, a spell that can reverse the dark magic used to create the Horcrux in the first place.
Well, it could be that Dumbledore, in some fanfic versions, figures it out first and then reveals it to Harry. Dumbledore is often portrayed as having a deep understanding of magic. He might have noticed some strange magical patterns or behaviors related to Harry that led him to suspect and then confirm that Harry was a Horcrux. And then he would tell Harry about it, which is how Harry comes to know.
Perhaps his father's old wand. It has a connection to his family and his heritage. Since it's a wand, it already has a certain amount of magical energy, so it could potentially be a suitable vessel for a Horcrux. And it would be a very interesting twist on the concept of a Horcrux as wands are not a typical choice.
One consequence could be that Harry feels an internal struggle. Since he has a part of Voldemort's soul in him, he might have to constantly fight against the dark impulses that come with it. For example, he may find himself having more aggressive thoughts or being more easily influenced by dark magic in certain situations.
One interesting concept is the idea of creating new Horcruxes. In some fanfictions, a character might attempt to create a Horcrux in a different way than Voldemort did, perhaps using a more unique object or spell. Another concept could be the destruction of Horcruxes in unexpected ways. For example, a fanfic might explore if a Horcrux could be destroyed by a powerful emotion rather than a specific magical weapon.
Well, he might be tempted by the dark magic within the Horcrux. It could try to manipulate him, maybe show him false visions of power or ways to defeat Voldemort that are actually leading him astray.