Preheat your air fryer to 375°F (190°C) for about 3 minutes, ensuring the basket is hot and ready for crisping.
While it heats, prepare the lemon butter by zesting and juicing the lemon into a small bowl, then melting the butter and mixing it with the lemon zest, juice, minced garlic, chopped herbs, salt, pepper, and red pepper flakes if using.
Pat the salmon fillets dry with paper towels to remove excess moisture, which helps achieve a crispy skin.
Use a basting brush to evenly coat the skin side of each fillet with a generous layer of lemon butter, focusing on the edges where splatter is likely.
Place the salmon filts skin-side down into the hot air fryer basket, ensuring they are spaced apart for proper air circulation.
Cook the salmon at 375°F (190°C) for 8–10 minutes, listening for the sizzling and crackling sounds as the skin crisps up and releases a fragrant aroma.
Check the salmon around the 8-minute mark; the skin should be golden and crispy, with a slight puff of steam when you open the basket.
Use tongs or a spatula to carefully lift the fillets out of the basket, revealing shiny, flaky flesh beneath the crispy skin.
Transfer the salmon to a plate, spoon any remaining lemon butter over the top, and garnish with extra herbs and lemon slices if desired.
Serve immediately to enjoy the full crunch of the skin and the warm, lemony butter melting into the tender fish.
