Preheat oven to 400°F (200°C). Rub potatoes with olive oil and salt, then place directly on oven rack and bake 50–60 minutes until tender.
Remove potatoes from oven and let cool slightly.
In a skillet over medium heat, melt butter and sauté garlic for 30 seconds until fragrant.
Add shrimp, Cajun seasoning, smoked paprika, black pepper, and red pepper flakes. Cook for 2–3 minutes until shrimp turns pink.
Reduce heat, stir in heavy cream and cream cheese until smooth and slightly thickened.
Add cheddar and mozzarella cheese, stirring until melted.
Gently fold in crab meat and green onions, then remove from heat.
Slice tops off the potatoes lengthwise and carefully scoop out most of the flesh, leaving sturdy shells.
Mash the potato flesh lightly and mix into the seafood filling.
Spoon filling back into potato shells and top with extra shredded cheese.
Place stuffed potatoes on a baking sheet and bake for 10–15 minutes until bubbly and golden.
Garnish with green onions or parsley and serve hot.