Preheat oven to 425°F (220°C). Cut potatoes into ¼-inch sticks, toss with the vegetable oil, Cajun seasoning, garlic powder, onion powder, smoked paprika, and salt. Spread across 2 sheet pans and roast for 25 to 30 minutes, flipping once at 15 minutes, until the edges are deep golden and the surface looks blistered.

While fries roast, melt butter in a small saucepan over medium-low heat. Whisk in flour and cook for 1 minute. Gradually whisk in milk and cook for 2 to 3 minutes until thickened. Remove from heat and stir in shredded cheddar and cayenne until smooth.

Remove fries from the oven, taste, and add more salt if needed. Transfer to a large serving dish in a loose pile.

Spoon cheese sauce over the fries, drizzle the ranch in a zigzag across the top, add the pickled jalapeños, scatter the green onions, and finish with dashes of hot sauce. Serve immediately.