Preheat your air fryer to 400°F to ensure the basket is hot for maximum crispiness.
Slice the russet potato into thin, even strips and toss them in a bowl with 0.5 tbsp of avocado oil and a pinch of sea salt.
Place the potato strips in the air fryer basket and cook for 15 minutes, shaking the basket halfway through until they are golden and tender.
While the fries cook, whisk together the light beer and arrowroot starch in a shallow dish until the batter is smooth and slightly bubbly.
Pat the cod fillets dry with a paper towel and season both sides with the garlic powder, paprika, sea salt, and black pepper.
Dip each seasoned fillet into the beer batter to coat thoroughly, let the excess drip off, and lightly mist with the remaining avocado oil.
Move the fries to one side of the air fryer basket and place the fish on the other side, then air fry for 10-12 minutes until the fish is opaque and the coating is shattered-crisp.