Preheat your air fryer to 400°F and line a separate baking sheet with parchment paper if using an oven for the potatoes.
Slice the Russet potato into thick wedges, toss with avocado oil, paprika, and a pinch of sea salt, then air fry or roast for 20 minutes until crispy.
Pat the cod fillet completely dry with paper towels to ensure the batter adheres properly for a crunchy finish.
In a small bowl, whisk together the arrowroot powder, garlic powder, and cold light beer until a smooth, thin batter forms.
Dredge the fish in the batter, letting any excess drip off, then place in the air fryer basket sprayed lightly with oil.
Air fry the fish for 10-12 minutes, flipping halfway through, until the coating is golden and the fish flakes easily with a fork.
Serve the hot fish alongside the potato wedges with a fresh lemon wedge for a bright, zesty finish.