Preheat your air fryer to 400°F (200°C).
Slice the russet potato into even wedges, then toss them in a bowl with 0.5 tbsp of avocado oil, sea salt, and paprika until well coated.
Arrange the potato wedges in a single layer in the air fryer basket and cook for 15-20 minutes, shaking halfway through, until they are crisp and golden.
While the potatoes cook, pat the cod fillets completely dry with paper towels and season both sides with garlic powder and black pepper.
In a small shallow bowl, whisk together the arrowroot powder and light beer until a smooth, thin batter forms.
Dip each seasoned cod fillet into the beer batter, allowing any excess to drip off, then lightly brush or spray the exterior with the remaining avocado oil.
Place the fish in the air fryer basket (working in batches if necessary) and cook at 375°F for 10-12 minutes until the coating is crunchy and the fish flakes easily with a fork.
Serve the hot crispy fish alongside the potato wedges with a fresh lemon wedge for a bright, citrusy finish.