Place the squash in a large bowl and toss with the oil, salt, cinnamon, and pepper. Keep the bowl handy, no need to wipe it out.
Place the squash in an air fryer basket. Air fry at 375°F until the squash is fork tender and lightly browned in places, about 22 to 25 minutes. Starting at the 10-minute mark, remove the basket and toss the squash, then toss a few more times at it nears the end of the cook time. Note that if your air fryer basket is small, you may need to extend the cooking time.
Transfer the squash back to the bowl you used to toss it with the oil and spices. Toss with the maple syrup, rosemary, and a pinch of additional salt to taste. Enjoy warm.
TO STORE: Store leftover air fryer butternut squash in an airtight storage container in the refrigerator for 4 to 5 days.
TO REHEAT: Reheat over low heat in a skillet on the stovetop, in the air fryer, or in the microwave until warmed through. You can also eat the squash cold or at room temperature, which is great in a salad.
TO FREEZE: Freeze the squash in an airtight freezer-safe storage container for up to 3 months. Thaw in the refrigerator the night before reheating.