Preheat your air fryer to 400°F (200°C) to ensure a hot cooking environment.
Slice the russet potato into even wedges, pat them dry, and toss with half of the avocado oil, salt, and pepper.
Place the potato wedges in the air fryer basket in a single layer and cook for 15-18 minutes, shaking halfway through, until they are golden and crisp.
While the fries cook, pat the cod fillets extremely dry with paper towels and season with a pinch of salt.
In a small mixing bowl, whisk together the flour, baking powder, remaining salt, pepper, and light beer until a thick, smooth batter forms.
Remove the fries from the air fryer and keep warm; lightly grease the basket with the remaining avocado oil.
Dredge each piece of fish into the batter to coat thoroughly, then place carefully into the air fryer basket.
Air fry the fish at 375°F (190°C) for 10-12 minutes, flipping gently at the halfway mark, until the exterior is crunchy and the fish is opaque.
Serve the hot fish and fries immediately with a fresh lemon wedge for a bright finish.