In some fanfictions, Harry might be ostracized post - war because people are jealous of his fame. He defeated Voldemort and became a hero, but some might resent his status and try to push him aside.
In some fanfictions, Harry simply ignores the ostracism. He focuses on his own life and continues to do what he believes is right, whether it's helping out at Hogwarts or exploring the wizarding world on his own.
It's popular because it creates a lot of drama. People like to see their favorite characters face challenges, and being ostracized is a huge one. It adds depth to Harry's character as he has to deal with loneliness and betrayal.
One example could be a fanfiction where Harry discovers he has a new and strange power that others in the wizarding world fear. As a result, they ostracize him, thinking he's a threat. For instance, if he could control time in an unpredictable way and the Ministry of Magic, fearing chaos, isolates him.
Another possible betrayer could be a jealous friend. For example, Neville might feel overshadowed by Harry throughout the war. After the war, this jealousy could turn into resentment, and he might do something to harm Harry's reputation, thus betraying him.
One great post - war Naruto Harry Potter fanfiction is 'The Crossover Chronicles'. It combines the magic of the Harry Potter world with the ninja skills of Naruto in a really interesting way. The characters from both universes interact in a post - war setting, which makes for some exciting plotlines.
He might start off being a bit of an outsider. The Avengers are used to a certain type of hero, and Harry with his magic would be very different. But he could win them over with his courage and loyalty, much like he did with his friends at Hogwarts.
One popular 'Harry Potter ostracized' fanfiction is 'The Outcast of Gryffindor'. It explores a scenario where Harry is wrongly shunned by his housemates. Another is 'Alone in Hogwarts' which delves into his feelings of isolation. There's also 'Ostracized Savior' that shows how Harry copes when he's pushed to the fringes of the wizarding community.
One reason could be that it adds a new layer of drama. The original story has Harry as a hero, but in these fanfictions, making him ostracized creates more conflict. It gives writers a chance to explore different aspects of his character, like his resilience.
You can check out 'Harry's Struggle in Peace'. It's a fanfic that focuses on Harry's inner turmoil after the war. He's suffering from PTSD and has a hard time adjusting to a world without Voldemort. The fic shows his journey of trying to find meaning in his life again.