Pat scallops dry. Season both sides with salt and pepper. Set aside.
Make your alfredo sauce. Melt 6 tbsp butter over medium heat. Add garlic and cook until golden and fragrant, about 2-3 minutes. Vigorously whisk in flour until no longer clumpy. Slowly stream in milk, whisking constantly. Heat mixture gently until slightly thickened, about 2-3 minutes more, then stir in parmesan cheese. Season with salt and pepper. Lower heat to the lowest setting possible on your stovetop. Cover and keep warm, stirring occasionally, as you prepare the rest of the meal.
Bring a large pot of salted water to a boil. Cook fettuccini according to package directions. Reserve 1/4 cup of the cooking liquid before draining. Toss pasta in pan with alfredo sauce. Cover and keep warm.
Prepare a plate with a layer of paper towels. Heat 1 tbsp butter and olive oil over medium-high heat until almost smoking. Carefully add scallops and seat 1 minute 30 seconds to 2 minutes. Flip scallops and swirl remaining tablespoon of butter around the pan. Sear opposite side for an additional 1 minute 30 seconds. Remove to the plate with paper towels.
To the same skillet, toss in broccolini and char for 2 minutes on one side, then flip and cook 2 more minutes. Toss with red pepper flakes, salt, and pepper.
To plate, divide stalks of broccolini amongst 6 plates. Top with swirls of fettucini alfredo, then top with sea scallops. Serve with additional parmesan and fresh thyme sprigs, as desired.