Preheat your air fryer to 400°F (200°C) to ensure a hot cooking environment for the fries.
Slice the russet potato into thin, even matchsticks and toss them in a bowl with 0.5 tbsp of olive oil and a pinch of sea salt.
Arrange the potatoes in a single layer in the air fryer basket and cook for 15 minutes, shaking halfway through, until they are golden and tender.
While the fries cook, whisk together the flour, baking powder, garlic powder, paprika, and light beer in a shallow bowl until a smooth batter forms.
Pat the cod fillets completely dry with a paper towel and season both sides with the remaining sea salt and black pepper.
Dredge each cod fillet through the beer batter, ensuring they are fully and evenly coated.
Lightly grease the air fryer basket with the remaining 0.5 tbsp of olive oil and place the battered fish inside.
Lower the temperature to 375°F and air fry the fish for 10-12 minutes until the coating is crunchy and the fish flakes easily with a fork.