The Galar starters are given to you as a gift at the start of Sword and Shield, in a standard PokeBall. Because they cannot be caught in the wild or in Max Raids, you cannot capture them in a ball other than a PokeBall.
If you're trying to breed a different ball onto a Galar starter, that too is impossible. If you're breeding with Ditto, the non-Ditto Pokemon will pass down the Ball -- in the starters' case, this will always be a PokeBall. If you breed a female starter with another Pokemon in the Egg Group, the female is the one to pass down the ball, meaning the offspring will be a Galarian starter... in another PokeBall.
As of now, it's impossible to have a Galarian starter in anything except a PokeBall. This could change in the future, however, and there is a precedent: Alolan starters were made available in Max Raid battles in these games, allowing them to be caught in other balls for the first time.
