Wash and peel the russet potatoes. Cut them into evenly sized fries, about 1/4-inch thick. Pat them dry with a paper towel to remove any excess moisture.
Place the cut potatoes in a large bowl of cold water and let them soak for about 30 minutes. This helps remove excess starch and promotes crispiness.
After soaking, drain the potatoes and pat them dry again with a paper towel.
In a separate bowl, combine the cornstarch, salt, paprika, garlic powder, and onion powder. Mix well to evenly distribute the seasonings.
Place the dried potato fries in a large zip-top bag or a bowl. Add the vegetable oil and toss to coat the fries evenly. Make sure each fry is coated with a thin layer of oil.
Sprinkle the seasoning mixture over the oiled fries. Close the zip-top bag (if using) or toss the fries in the bowl to coat them with the seasoning mixture.
Lightly grease the air fryer basket or tray with cooking spray or a small amount of oil. This will help prevent the fries from sticking.
Arrange the seasoned fries in a single layer in the air fryer basket or tray, ensuring they are not overcrowded. You may need to cook them in batches depending on the capacity of your air fryer.
Cook the fries in the air fryer at 400°F (200°C) for approximately 15-20 minutes, flipping them halfway through the cooking time. Adjust the cooking time as needed based on your desired level of crispness.
Once the fries are golden brown and crispy, remove them from the air fryer and let them cool for a few minutes.
Serve the air fryer Wendy's copycat french fries immediately with your favorite dipping sauce or enjoy them as is.