Whisk together sour cream, lemon juice, and ¼ tsp. salt; set aside for serving.
Whisk flour, baking powder, Old Bay seasoning, and ½ tsp. salt in a large bowl. Whisk egg and buttermilk in a medium bowl, then add to dry ingredients and stir to combine. Stir in scallions, jalapeño, shrimp, corn, and cheese.
Heat 2 Tbsp. oil in a large skillet over medium. Working in batches and adding more oil in between, drop ¼-cupfuls corn mixture into skillet, flattening slightly, and cook until golden and crisp, about 4 minutes per side. Transfer fritters to paper towels to drain; season with salt and serve immediately with sour cream sauce and lemon wedges alongside.
