One common theme is friendship. Sonic and Sonic (even if they are different versions) often form a unique bond, and their friendship with Amy is explored in different ways. It could be about how they support each other through tough times.
For Amy, she could become more understanding of the 'evil' or opposing side. Instead of just seeing Metal Sonic as a bad guy, she might learn to look deeper into his existence as a creation. This could make her more empathetic in general.
One popular Sonic X Amy Sonic Boom fanfiction could be 'Amy's Adventure in Sonic Boom World'. It might focus on Amy's experiences in the Sonic Boom universe within the context of her relationship with Sonic from Sonic X. Another could be 'Sonic and Amy: A New Chapter' which could explore how their relationship from Sonic X might develop in the Sonic Boom setting.
You can try looking for it on official gaming platforms or related game websites. Sometimes, they have direct links or instructions for accessing new stories.