Why does Juan fear for Mariana's safety even in
"that hidden Paris neighborhood"?

Incomplete question. However, I infer you are referring to the story "The Censors".

Likely because of his background.

Explanation:

More likely his background affected his concern for Mariana. Probably be had experienced government censorship of information where he lived, and so thought it was in such neighborhood that Mariana lived.

However, Mariana was in a hidden Paris neighbourhood likely different from Juan's own.

well, there are online sites that can make it look like a texting screenshot, so u can make it like hamilton texting jefferson through that, and he can start with him being like, i know it's out of the blue, but blah blah blah

she needs to add a conclusion summing up the entire essay along with an ending sentence to complete it all nicely.