As we've said, Marinette Dupain-Cheng lives in Paris. According to the show's press kit, she lives in the 21st Arrondissement, which is a bit of a joke: Paris only has 20 arrondissements, so it's like saying Peter Parker is from the sixth borough of New York City, "Hudson Park." But real landmarks appear in the series (take a drink every time the solution involves going to the Eiffel Tower for no reason), so you can attempt to pin down where she actually lives.
On the micro scale, Episode 2 of the series shows an aerial view of the neighborhood, revealing that pretty much all the major character locations (Marinette's house, Adrien's house, Chloe's house, and the school) are within a block of one another. That may seem like an exaggeration, or something thrown together quickly to fake a city layout, but various street views throughout the series remain fairly consistent about the relationship of those buildings. It's the rest of the city that just gets dropped wherever is convenient.
For example, Marinette's house is located on the corner of a park, and the buildings in the background make it clear it's based on the Place des Vosges, which would put it right on the line between the 3rd and 4th arrondissements, on the right bank of the Seinne.
Unfortunately, Notre Dame cathedral can be seen from Marinette's front door and roof, which would put her somewhere south in the 5th, on the left bank. (There's also a bridge directly across from her, right at the rear of the cathedral, that doesn't exist in real life.)
According to the sky view, Adrian's house is right across the street from the back of Marinette's park. Okay, sure. But visible from his front door is the Fontaine du Palmier, meaning he lives right behind the Place du Châtelet and the Pont au Change, on the border between the 1st and 4th arrondissements. You can even make it out on that overhead shot. Sometimes the Eiffel Tower can be seen immediately behind his house (to the north), despite being way way way to the west and on the opposite bank of the river.
Around the corner from the Agreste Mansion is Le Grand Paris, the hotel owned by the Bourgeois family. It's visually based on the real life Hôtel Plaza Athénéé (the red awnings and wrought iron balcony rails are a clear giveaway), which is to the west, closer to the Eiffel Tower than anything else. The real hotel is much larger, but at least the Eiffel Tower could be visible behind Adrian's house here?
Right across the street from Marinette's home is her school, Collège Françoise Dupont, named after France's first female superhero. Creator Thomas Astruc has said it's based on on Lycée Carnot, an actual high school in the 17th arrondissement, to the northwest of the city center, but that seems to be more the interior than the exterior.
Finally, the big surprise is that the Dupain-Cheng bakery is based on a real place!
At 48 Rue Caulaincourt, far north of the Seinne in the 9th arrondissement (near the John Wick steps), you'll find the Boris Lumé Boulangerie, the direct visual inspiration for Marinette's home.
Built in 1900, the building is on the historical registry; other than the style of roof, it's a pretty direct copy! The really wild thing is the bakery is owned by a native Frenchman (that'd be Boris, obvs) and his wife, Mihona!
Okay, she's Japanese rather than Chinese, but still. If an evil butterfly man starts threatening the city, I think we know where to go for help.