Preheat your air fryer to 400°F (200°C) to ensure a hot cooking environment for maximum crunch.
Slice the russet potato into thin, uniform wedges and toss them in a bowl with the avocado oil and half of the sea salt and black pepper.
Place the potato wedges in the air fryer basket in a single layer and cook for 15 minutes, shaking the basket halfway through.
While the potatoes cook, pat the cod fillets extremely dry with paper towels to help the batter stick.
In a shallow dish, whisk together the gluten-free flour, arrowroot starch, garlic powder, and the remaining salt and pepper.
Slowly pour the cold light beer into the dry ingredients, whisking gently until a smooth, thick batter forms.
Dip each cod fillet into the batter, allowing any excess to drip off, then carefully place them in the air fryer basket alongside the potatoes.
Air fry everything for an additional 10 to 12 minutes, flipping the fish once, until the coating is shatteringly crisp and the fish is opaque.
Serve the fish and chips immediately with a fresh lemon wedge for a bright, zesty finish.