Step by step guide on how to easily catch an Alpha Pokémon in Pokémon Legends Arceus:
1) Try to take cover in a patch of grass
2) Lock on to the Pokémon to determine what it’s preferred foods are
3) Make a cake using one of the ingredients from the preferred foods list (in this case it liked honey so made a honey cake)
4) Try to throw it away from nearby Pokémon
5) As it’s eating, sneak up behind with the most upgraded version of the heavy ball you have. You can determine if it will be an easier catch by the color of the Poke ball logo. As shown in this video, a green color indicates an easier catch.