Preheat the air fryer to 400°F (200°C).
Slice the russet potato into thin wedges and pat them dry with a paper towel to ensure maximum crispness.
Toss the potato wedges in a bowl with the olive oil and half of the sea salt and black pepper.
Place the potatoes in the air fryer basket and cook for 15-18 minutes, shaking the basket halfway through, until golden brown.
While the potatoes cook, season the cod fillets with the garlic powder, paprika, and the remaining salt and pepper.
In a shallow bowl, whisk together the flour, cornstarch, and cold light beer until a smooth, thick batter forms.
Dip each cod fillet into the batter, allowing any excess to drip off before placing them into the air fryer basket.
Cook the fish at 375°F (190°C) for 10-12 minutes, flipping carefully halfway through, until the coating is crunchy and the fish flakes easily.
Serve the crispy fish immediately alongside the hot potato wedges.