Preheat your air fryer to 400°F (200°C) to ensure it is hot enough for maximum crispiness.
Slice the russet potato into thin wedges, then toss them in a bowl with half of the avocado oil and a pinch of sea salt.
Place the potato wedges in the air fryer basket in a single layer and cook for 15-20 minutes, shaking halfway through, until they are golden brown and crisp.
While the potatoes cook, pat the cod fillets completely dry with paper towels and season both sides with sea salt, black pepper, garlic powder, and paprika.
In a shallow bowl, whisk together the arrowroot starch and light beer until a smooth, thin batter forms.
Dip each seasoned fish fillet into the batter, allowing any excess to drip off before placing them into the air fryer basket (lightly greased with the remaining avocado oil).
Air fry the fish at 375°F (190°C) for 10-12 minutes, flipping gently halfway through, until the coating is golden and the fish flakes easily with a fork.