FOR THE FISH AND FRENCH FRIES:
FOR THE TARTAR SAUCE:
Heat air fryer to 400°F for 10 minutes. Coat the air fryer basket with cooking spray. Working in batches if needed, place 1 pound frozen steak fries in a single layer in the air fryer basket. Air fry for 6 minutes. Flip the fries and air fry until crispy, 6 to 8 minutes more. (Final cook time will depend on your air fryer's capacity and the thickness of your fries.)
Meanwhile, place 1 1/2 cups panko breadcrumbs and 1 teaspoon of the kosher salt in a shallow dish and stir to combine. Place 1/3 cup all-purpose flour, the remaining 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper in a second shallow dish and stir to combine. In a third shallow dish, lightly whisk together 2 large eggs and 2 tablespoons water.
When the fries are ready, transfer to a serving bowl and season with kosher salt. Tent the bowl loosely with aluminum foil to keep warm. Reduce the air fryer temperature to 375°F.
Halve 4 cod fillets lengthwise into 2 long strips. (There will be a total of 8 pieces.) Working with one stirp at a time, dredge in the flour mixture and shake off the excess. Dip in the egg mixture and let any excess drip off. Dredge in the panko mixture, pressing it in to adhere. Place on a baking sheet or plate.
Working in batches if needed, place the fish in a single layer in the air fryer basket. Air fry until golden and crispy, flipping halfway through, about 12 minutes total. The thicker parts of the cod fillet will take longer to cook than the thinner parts toward the tail of the fish, so you may need to cook thicker pieces longer. Meanwhile, make the tartar sauce.
Place 1/2 cup mayonnaise, 1 teaspoon relish, 1/2 teaspoon Dijon mustard, and 1/2 teaspoon lemon juice in a small bowl and whisk to combine.
To serve, place 2 pieces of fish and some steak fries on a plate or arrange inside a newspaper cone. Serve with lemon wedges, malt vinegar, and the tartar sauce.