Can You Get Shiny Starters in ‘Pokémon Scarlet’ and ‘Violet’?

Though you won’t be able to get a Shiny Quaxly, Sprigatito, or Fuecoco at the start of the game, you will be able to get the Shiny Pokémon through breeding later on in the game.

If you breed a female starter Pokémon with a Ditto, you have a chance of hatching a Shiny starter Pokémon — though again, the odds for finding a Shiny Pokémon are low, and you’ll likely have to hatch multiple eggs before finding that Shiny starter.

Source: https://www.distractify.com/p/can-you-get-shiny-starters-pokemon-scarlet-violet