Preheat your air fryer to 400°F.
Slice the russet potato into thin wedges and toss them in a bowl with the olive oil and half of the sea salt and black 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 potatoes cook, whisk together the arrowroot powder, light beer, paprika, garlic powder, and the remaining salt and pepper in a shallow bowl until a smooth, bubbly batter forms.
Pat the cod fillets completely dry with a paper towel, then dip each piece into the batter until thoroughly coated.
Remove the potatoes from the air fryer and set aside; lightly grease the basket and place the battered fish inside.
Air fry the fish at 375°F for 10-12 minutes, flipping gently halfway through, until the coating is crunchy and the fish flakes easily with a fork.
Serve the crispy fish alongside the potato wedges with a fresh lemon wedge for squeezing over the top.