Preheat oven to 375°F (190°C). Cook lasagna noodles per package instructions, drain, and lay flat on parchment.
Sauté garlic in olive oil over medium heat for 1 minute. Add shrimp and cook 3–4 minutes until pink. Stir in crab, salt, pepper, and red pepper flakes; cook 2–3 more minutes. Remove from heat.
Combine ricotta, 1 cup mozzarella, 1/2 cup Parmesan, heavy cream, and parsley in a bowl. Stir until smooth.
Spread Alfredo sauce in a 9x13 dish. Add noodles, 1/3 cheese mixture, 1/3 seafood, and more Alfredo. Repeat for 3 layers.
Top with remaining mozzarella, Parmesan, and breadcrumbs.
Cover and bake 25 minutes. Uncover and bake 10–15 minutes until golden. Let rest 10 minutes before serving.