Hard boil the eggs using your preferred method:

Cold Water Start: Place eggs in a pot. Add cold water to 1" above the eggs. Heat until the water starts boiling. Remove from heat. Cover pan. Let sit for 22-24 minutes. Remove eggs from the water, rinse under cold running water, or add to an ice bath for 5 minutes.

Instant Pot Method: Place 1 cup of cold water in the Instant Pot. Add a trivet and place the eggs on it. Check the seal, and that vent is on sealing. Cook on Manual, High Pressure for 7 minutes. When time is up, Quick Release the pressure. Remove eggs and rinse under cold running water. Then place the eggs in a bowl of ice water for 10 minutes.

Air Fryer Method: Preheat an air fryer to 250°F/120°C. Place eggs into the air fryer basket, and cook for 15 minutes. Transfer to a bowl of icy water for about 10 minutes until they are fully cooled.

Peel and chop the eggs, and add to a mixing bowl with finely chopped celery, 3 tablespoons of mayonnaise, mustard, and horseradish. Mix together gently, and add salt, pepper, and chives to taste.

Slice croissants in half. Place a lettuce leaf on the bottom half, and top with egg salad. Add the croissant tops and place the assembled sandwiches onto a platter. Serve as desired with vegetable crudites and dip. Enjoy.