Yes, it's possible. Some fanfiction authors might incorporate elements like the British national anthem 'God Save the Queen' into their stories for various reasons. It could be to add a touch of British authenticity, or to create a specific mood related to the wizarding world's connection to the Muggle (British) society.
Well, it's special because it extends the magic. The Harry Potter series left many things open - ended, and fanfiction fills those gaps. For example, we can see how the wizarding world recovers after the final battle in different fanfictions. It's a platform for creativity where fans can put their own spin on the well - loved story. They can introduce new magical creatures or spells, making the world even more fantastical.
One way could be to have it play during a Quidditch match that has a special international or Muggle - related event. Another way is to have a wizard or witch who is a big fan of Muggle culture and they sing it during a celebration at Hogwarts.
You can start by looking on fanfiction.net. It has a large collection of Harry Potter fanfictions. There are also some really good ones on Archive of Our Own (AO3). AO3 has a great tagging system which makes it easier to find specific types of fanfictions, like those focused on a particular character or time period in the Harry Potter universe.
Perhaps Harry sees a bit of himself in Atreus. Atreus is on a journey of self - discovery and growth, much like Harry was during his years at Hogwarts. Harry could be drawn to Atreus' courage and determination, and so he decides to save him when he's in trouble. It could also be that Harry is just exploring this new and strange world of God of War and when he comes across Atreus, he feels compelled to protect him as he would any other innocent in his own world.
In some fanfictions, Harry might use his magic skills. For example, he could use spells to protect Naruto from a powerful enemy. Maybe he casts a shield charm to block an attack that Naruto couldn't avoid on his own.
Well, 'The Ascension of Harry' is a fanfiction where Harry becomes a god. This happens when he discovers an ancient magical artifact that grants him divine abilities and a new destiny.
Harry Potter might save the Avengers by using his magic to teleport them away from danger. He could use Apparition or the Floo Network if he could somehow make it work in the Avengers' world.
Well, it might start with Harry Potter getting into a real pickle. For example, he could be framed for a crime he didn't commit and on the run from the Ministry of Magic. The goblins, who have their own agenda and a sense of justice, decide to help him. They might hide him in their Gringotts vaults or use their magic to create a diversion. It could also be that the goblins are repaying a debt to Harry, or they see a greater threat that Harry's survival can help to prevent in the wizarding world.
In some fanfictions, Harry Potter might use his magic skills. For example, he could cast protective spells to shield the Winchesters from supernatural threats. His knowledge of the magical world could also help them find solutions to problems they face in their world of hunting monsters.