Can you get anything with 40 species of Pokemon on the pokedex?

Yes, you can get the national Pokedex in the game Pokemon Sword and Shield by:

1. Completing the Galar Pokedex (all 400 Pokémon)

2. Defeating Leon and becoming the Pokemon Champion

3. Speaking to Sonia in her lab in Postwick after she finishes her research

4. Receiving the National Pokedex from Sonia