Pat the steak cubes thoroughly dry with paper towels. Season evenly with salt, black pepper, and smoked paprika.
Heat a large cast-iron or heavy skillet over medium-high heat. Add the olive oil and 1 tablespoon of butter.
Once the skillet is hot, arrange the steak pieces in a single layer, leaving some space between them. Work in batches if your skillet is too small.
Sear the steak for about 1–2 minutes per side, turning the pieces until they are deeply browned and cooked to your preferred doneness. Transfer the steak to a plate.
Reduce the heat to medium-low. Add the remaining 3 tablespoons of butter to the skillet.
Add the minced garlic and thyme. Cook for about 30–60 seconds, stirring frequently, just until the garlic becomes fragrant.
Return the steak bites and any accumulated juices to the skillet. Toss everything in the garlic butter for about 30 seconds until evenly coated and warmed through.
Remove from the heat, sprinkle with fresh parsley, and add red pepper flakes if desired. Serve immediately with your favorite side dishes.