If you just want 1-2 s'mores for a quick snack, the air fryer is ideal and no preheating is necessary. Use vegan graham crackers and vegan marhsmallows for a vegan treat.
Balance marshmallow on top of chocolate. You can also cut the marshmallow in half if you prefer.
Gently push the basket into the air fryer so it locks into place. Be careful not to shove the basket and make the chocolate and marshmallow fall off the cracker.
Set temperature to 350 degrees F and time for 1 minute. Use the 'Air Fry' setting in case your air fryer has options.
When the timer goes off, gently pull out the air fryer basket and check the brownness of the marshmallow. it should be slightly golden and puffed. (At this point, you could air fry further for more golden brownness, but you risk burning the graham cracker and causing the chocolate to melt too much.)
Carefully remove the s'more from the hot air fryer. Top the s'more with the second cracker.
Let cool for a minute before eating. When eating, note the chocolate may be melted and scalding hot, so bite carefully.
Notes
You can fit up to 4 graham crackers in the a 6 qt air fryer comfortably, without touching each other. You need space for the marshmallow to puff and also room to maneuver them out of the air fryer.
If you do cook 4 s'mores at a time, the time and temperature settings are the same. No adjustment needed to cook more s'mores.
No preheating is necessary. You can put the the s'mores into a cold air fryer. If you have an air fryer that beeps at you when it's finished preheating, just ignore. Remove the s'mores once the 1 minute timer after preheating is completed.
Conversely, you can also start with a hot air fryer that's already preheated. The time and temperature are the same whether you start with a hot or cold air fryer.
You do not need to rotate or turn the s'mores halfway through cooking, even if the air fryer beeps at you (like the Instant Vortex does).
The vegan marshmallows brand from Dandies develops a shiny, hardened thin crust when heated, so just note the 2nd graham cracker won't really stick to it and may slide off.