Mix the popcorn, almonds, and pretzels in a large baking sheet, air fryer basket, or tray bowl.
Melt the butter, brown sugar, salt, and vanilla together over medium heat until it boils in a medium pot. Boil for 5 minutes (a candy thermometer should reach 240° F), then immediately mix in the vinegar and baking soda, whisk well.
Pour the caramel mixture over the popcorn mixture and stir to coat.
Transfer the sheet pan to the air fryer basket or tray, and air fry for 4 to 6 minutes, at 250 degrees F, air fryer setting, stirring occasionally. Remove from oven and let cool 2-3 minutes before stirring in the chopped chocolate bar and marshmallows.
Allow cooling completely before dividing into lidded containers. The caramel corn will keep for about 7 days at room temperature.