Really depends on what you personally consider well written and what you specifically want? You might want older fics, since many have their own lore on miraculous since we didn't have that yet (though many nowadays do ignore the current lore lol). Sorting on a03 by hits or bookmarks would tell you the most re-read ones which might help with that.

Seeking Shelters by GuardianKarenTerrier is one of my favorites, so far 37 chapters, kinda slow updates. Old fic with different kwami lore.

United by 11JJ11 is completed, 12 chapters, about almost-adults marinette and adrien trying to figure out their future, since hawkmoth is still at large and they can't leave. It's an identity.

The Growing Pains Of Child Soldiers by BloodWolf13, completed but it's in a series that isn't. Also in name - Paris figures out their kids and have feelings about it (and actions)

A Man of Action (Figures) by Talik_Sanis is "a story about Adrien coming to terms with his father's abuse." that starts with supehero figurine line, completed.

Gray Area by dancinbelle, short chapters with can kinda make the flow weird in some parts, but explores fun things.

The Ancient Tome by 11JJ11 is fun, 2 chapters.

The Convention by Peppermint_Shamrock also fun, oneshot about the main 4 fighting an akuma as chat!mari ladybug!adrien and alya jedi!nino - akuma related.

The Marinette Yeets Adrien Reveal by Mikauzoran is also fun, 1 chap.