Preheat your air fryer to 400°F (200°C) to ensure a hot cooking surface.
Slice the russet potato into thin, uniform wedges and toss them in a bowl with 1 teaspoon of avocado oil and the garlic powder.
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 crispy.
In a small mixing bowl, whisk together the flour and light beer until a smooth, thick batter forms.
Pat the cod fillet completely dry with paper towels, season with sea salt and black pepper, then dip the fish into the batter to coat all sides thoroughly.
Lightly brush or spray the battered cod with the remaining 1 teaspoon of avocado oil and place it in the air fryer basket.
Cook the cod at 375°F (190°C) for 10-12 minutes, gently flipping once, until the crust is golden-brown and the fish flakes easily with a fork.
While the fish cooks, stir together the Greek yogurt, lemon juice, and finely chopped capers in a small bowl to create the high-protein tartar sauce.
Serve the hot beer-battered cod immediately alongside the hand-cut fries and the chilled yogurt sauce.