Reading those Maxon POV fics is like getting a decoder ring for the whole selection. You get this internal monologue full of royal protocol anxiety and the absolute whiplash of meeting thirty-five strangers who are supposed to be his future wife. A huge trope I see is the 'Secretly Smitten from Day One' angle, where he notices America instantly but feels he has to be impartial, so every interaction with her is analyzed to death in his head while he's trying to be polite to the others.
Another big one is the 'Burdened Crown' introspection. Fics love to explore his relationship with his father, King Clarkson, painting Maxon as someone trapped between his own gentler instincts and the harsh, manipulative tactics he's been taught. You'll see a lot of scenes of him alone in his study, just weighed down by duty. There's also the 'Jealousy Realization' arc that's almost universal—where he slowly understands his frustration when America talks to Aspen isn't just about protocol, but actual jealousy, which is a feeling his royal education never prepared him for. It's all about grafting a modern emotional intelligence onto a character who, in the original books, we only see from the outside.
They also tend to expand on his friendships, like with the guards, showing a loneliness the public never sees. The trope of 'The Performer' is strong too; him constantly feeling like he's playing the part of the confident prince while internally he's a mess. It fills in all the gaps Kiera Cass left, which is basically the entire point of fanfiction.