What do you think of the oppressive atmosphere and aggressive joylessness as some kind of ultra-performative "mourning" for Emilie, esp. in no-Miraculous AU's?
I don’t read a whole lot of no-Miraculous AUs, so I’m passing on that part of the question.
We know Gabriel’s a control freak and, if anyone has ever in his life told him he can’t have things his way, that was a good long while ago. (My personal money is on he only ever heard such a thing from his father, and you will notice Adrien has never once mentioned grandparents.) If Gabriel cannot be happy, no one will. Not even, and he says this in almost so many words in “Party Crasher”, his own son.
But I do not think that’s performative, except in much the same sense that gender is inherently performative. I think those are Gabriel’s genuine emotions on display, if sometimes amped up for dramatic effect. Method acting.
Adrien I think is doing exactly the same thing, except that he is not generally content to wallow in anger and sadness and pain. The oppressive atmosphere of the Agreste household is mostly oppressing Adrien, who has long since learned the safest thing to do when Gabriel’s involved is whatever it is Gabriel wants. And whenever possible, Adrien is somewhere else, being happier, and often trying to make sure nobody else has reason to be angry or sad or hurt.