Another thread just reminded me of one of the "simulationy" things that bugs me in 5E especially: the pace of advancement is such that you can have a bunch of novice adventurers head off toward the dungeon, terrified of meeting goblins in the woods, and literally a week later return at 3rd or 4th level and not be one bit worried about the stuff that a week ago scared them to death. it just feels off to me. But if you make the monsters in the woods werewolves or trolls to ensure the PCs will still be worried a week later, you've created a deathtrap for them on the way out should the random encounter appear. Of course as GM you can always put your finger on the scale, but that itself is anti-simulation.
That last part is exactly why I don't like worrying about simulation, and also why I homebrew basically all my npcs. The goblins in the woods are still a worry for 4th level characters, they just have more ways of countering them.
Last night I ran a Strixhaven session in which the PCs met their dorm neighbors, chose and customized their rooms (I had the dorm rooms magically transform to accommodate their desires), and then head out together to the Bow's End Tavern.
The dorm is not described at all except to note that the centra campus has dorms, so I invented a circular building featuring an atrium in the center that houses a tree that stretches up past the roof of the 3 story building, with a couple rooms, kitchen, and common area at ground floor, and many rooms on the other floors. The archetecture is intentionally somewhat irrational, but there was a point where I had to say no to a request in order for the building to
work. My wife and our friend who were rooming together asked for a room with windows both to the atrium and to the outside of the building. The problem there is, where would the hallway go from which one enters the room? So, instead they have a balcony facing outward, and the
hallway on the inside has a small balcony into the atrium.
They played Wizard Gizzard, which was pretty boring tbh but that is partly on me. I did a lot of describing the game and then failed to fix the boring mechanics given in the adventure. After the game, the steam mephits attacked in the kitchen. Steam mephits are dirt boring, so I had them have a feature to transform their elemental type if they were bloodied with elemental damage that corresponds to a type of mephit, and if they were reduced to 0 in such a way, they'd make a con save that if they succeeded on, they'd reform the next round as a different kind of mephit. Only one mephit ended up changing, but it made the battle very memorable, and now there is a new thing in the world that the players can reference if they get a chance, because once established a thing like that always exists.
So, internal consitency, and basics of the world functioning on an everyday level, are all the simulation i care about.