Pokémon Sword/Shield give you extra rerolls to try to generate a shiny based on how many of the Pokémon you've ever battled, and how long your current encounter chain is. Shiny charm still gives +2 if obtained.
— Kurt (@Kaphotics) November 14, 2019
We're not sure what increments your chain counter, but this is it! pic.twitter.com/k5rX7tTcUf