Definitely not. AOT is a work of fiction that combines elements of fantasy, action, and drama. It's set in a made-up world with its own unique plot and characters.
Yes, there might be. Often game sequels like AOT 2 on platforms such as PS4 introduce new story elements. It could be related to new characters, new plotlines in the existing world of the game, or even side stories that expand the overall lore.
AOT is purely fictional. The story and its elements are the imagination of the creator. It doesn't draw from real-life events or people. It's a world crafted specifically for the anime and manga.
There could be various fanfictions. Maybe some that focus on alternative endings, like ones where certain characters survive who didn't in the original. For example, a fanfiction where Erwin survives and leads the Scouts in a different way.
One way is to check on popular fanfiction websites. Look for ones with high ratings and a lot of reviews. For example, Archive of Our Own (AO3) has a large collection of AOT fanfictions. You can search for the most popular ones there.
The AOT manga has finished. It wrapped up all the major plotlines and provided a conclusion to the story that fans have been following for a long time.