Bring a pot of salted water to a boil. Add the shrimp and cook until they turn pink and opaque about 2–3 minutes. Drain and rinse under cold water to stop the cooking.
In a glass jar, add half the lemon slices, half the onion slices, and half the dill.
Place the cooled shrimp on top of the first layer of ingredients in the jar.
In a bowl, combine the vegetable oil, vinegar, garlic, sugar substitute, mustard seeds, and red pepper flakes, stirring until the sugar substitute dissolves. Pour over the shrimp in the jar.
Layer the rest of the lemon slices, onion, and dill on top. Gently roll the jar to distribute the marinade without disturbing the layers.
Close the jar and refrigerate for at least 4 hours, ideally overnight.
Hard boil the eggs, cool them under cold water, then peel and chill until ready to serve.
Halve each egg carefully without disturbing the yolk. Add about 1/2 teaspoon of crème fraîche on each half.
Place a piece of pickled shrimp on each egg and garnish with a dill frond. Serve chilled.