Preheat your air fryer to 400°F for 5 minutes.
Slice the russet potato into 1/2-inch thick wedges, then toss them in a bowl with the olive oil, garlic powder, and a pinch of salt.
Place the potato wedges in the air fryer basket and cook for 15-18 minutes, shaking the basket halfway through, until they are golden and crispy.
While the potatoes cook, pat the cod fillet completely dry with paper towels and season both sides with salt and pepper.
In a shallow bowl, whisk together the flour, baking powder, and cold light beer until a smooth, thick batter forms.
Dip the seasoned fish into the batter, ensuring it is fully coated, and let any excess batter drip off.
Carefully place the fish in the air fryer basket (sprayed with a little oil) and cook at 375°F for 10-12 minutes, flipping once, until the coating is crunchy and the fish is opaque.
Serve the fish and chips immediately with a fresh lemon wedge on the side.