Preheat your air fryer to 400°F.
Slice the russet potato into thin wedges and toss them in a bowl with 0.5 tbsp of avocado oil and a pinch of the sea salt.
Place the potato wedges in the air fryer basket in a single layer and cook for 15-18 minutes, shaking the basket halfway through, until they are golden and crisp.
While the potatoes are cooking, prepare the batter by whisking together the arrowroot powder, garlic powder, paprika, black pepper, and the remaining sea salt in a shallow bowl.
Slowly pour the light beer into the dry mixture, whisking constantly until a smooth, thick batter forms.
Pat the cod fillets very dry with paper towels, then dip each piece into the beer batter until fully submerged and coated.
Remove the potatoes from the air fryer and set aside; place the battered fish into the basket and lightly mist with the remaining 0.5 tbsp of avocado oil.
Air fry the fish at 400°F for 10-12 minutes, flipping carefully halfway through, until the coating is browned and the fish flakes easily with a fork.