Scrub the sweet potatoes and dry them completely.
Place each potato between two wooden spoon handles. Slice straight down at 1/4-inch intervals, letting the handles stop the knife. Gently fan the slices apart.
Brush the potatoes with olive oil, working it down into the cuts. Season with sea salt and pepper. Tuck herbs into a few slices if using.
Preheat the air fryer to 350°F for 3 minutes.
Arrange the potatoes in a single layer in the basket. Air fry at 350°F for 20 minutes, brushing again with oil at the 10-minute mark.
While they cook, whip the softened butter, maple syrup, salt, and cinnamon together for about 1 minute until light and fluffy.
The potatoes are done when a fork slides in easily and the edges are dark and crisp. Rest 3–5 minutes.
Spoon the whipped maple butter over the top and serve warm.