Preheat your air fryer to 400°F (200°C) to ensure a high-heat environment for maximum crispness.
Wash and dry the russet potato, then slice it into even 1/2-inch thick wedges.
Toss the potato wedges in a bowl with avocado oil and a pinch of sea salt until evenly coated.
Place the wedges in the air fryer basket in a single layer and cook for 15-18 minutes, shaking halfway through, until golden brown.
While the potatoes cook, whisk the arrowroot powder, light beer, garlic powder, and paprika in a shallow bowl until a smooth, thin batter forms.
Pat the cod fillet extremely dry with paper towels, then season both sides with sea salt and black pepper.
Dip the cod into the beer batter, allowing any excess to drip off before placing it into the air fryer basket next to the potatoes.
Lower the air fryer temperature to 375°F (190°C) and cook the fish for 10-12 minutes, flipping gently halfway, until the coating is crisp and the fish flakes easily.
Serve the fish and chips immediately with a fresh lemon wedge for a bright, acidic finish.