Gymega Soup can both charge energy and degenerate energy, while Max Candy can only fill energy.
Gigantamax soup can make Pokémon with potential Gigantamax, and it can also cause Gigantamaxed Pokémon to degenerate into Pokémon with potential. If you give it to a Pokémon that can evolve to Gigantamax, it will lose its ability to Gigantamax and will only be able to Gigantamax. After giving Dynamax candy to a Pokémon, the Dynamax level can be increased by 1. When the Dynamax level increases, HP will increase.
Giant soup is a new prop in the "Pokémon: Sword and Shield" DLC: The Island of Armor, and it is a special dish. The Dynamax Candy is a type of candy that first appeared in Generation VIII.