Slice the russet potato into thin wedges and soak them in a bowl of cold water for 15 minutes to remove excess starch.
Drain and thoroughly pat the potato wedges dry with a clean kitchen towel.
Toss the potatoes with 1 teaspoon of avocado oil and half of the sea salt and black pepper.
Place the potatoes in the air fryer basket and cook at 400°F for 18-20 minutes, shaking the basket halfway through until golden and crisp.
While potatoes cook, whisk together the brown rice flour, garlic powder, paprika, and the remaining salt and pepper in a medium bowl.
Slowly pour the cold non-alcoholic beer into the flour mixture, whisking until a smooth, thick batter forms.
Pat the cod fillets dry with paper towels and cut into large strips.
Dip each piece of fish into the batter to coat completely, then place in the air fryer (use a parchment liner if needed) and lightly spritz with the remaining avocado oil.
Air fry the fish at 400°F for 10-12 minutes, flipping gently halfway through, until the coating is crispy and the fish flakes easily with a fork.
Serve the crispy fish alongside the potato wedges with a fresh lemon slice for squeezing.