Pat steak cubes and peeled shrimp completely dry with paper towels. Season steak cubes in one bowl with half of the salt, black pepper, and Italian seasoning. Season shrimp in a second bowl with remaining salt, pepper, and smoked paprika.
Heat 1 tablespoon olive oil and 1 tablespoon butter in a heavy 12-inch cast iron skillet over high heat until smoking hot. Add steak bites in a single uncrowded layer and sear without moving for 2 minutes to develop a deep brown crust. Flip and sear for another 1 to 2 minutes until medium-rare to medium (135u00b0F / 57u00b0C). Transfer steak bites to a clean plate.
Add another tablespoon olive oil to the same skillet over medium-high heat. Add seasoned shrimp in a single layer and sear for 1 to 2 minutes per side until pink, opaque, and slightly caramelized. Transfer shrimp to the plate with the steak.
Reduce skillet heat to low. Add the remaining 2 tablespoons butter to the pan drippings. As the butter melts and begins to foam, add minced garlic and crushed red pepper flakes. Sautu00e9 gently for 60 seconds until fragrant, swirling the pan to infuse the butter without burning the garlic.
Remove the skillet from direct heat. Stir in fresh lemon juice and chopped parsley, scraping up any delicious browned pan fond from the bottom.
Return seared steak bites and plump shrimp along with any resting juices back into the skillet. Spoon the foaming garlic herb butter generously over the steak and shrimp until glossy and evenly coated.
Serve immediately straight from the sizzling skillet with extra lemon wedges and warm crusty artisan bread for dipping!