First-Week Pokémon Brilliant Diamond and Shining Pearl Sales Roughly on Par With Sword & Shield; Around 6 Million Copies Sold Globally
https://wccftech.com/pokemon-brilliant-diamond-shining-pearl-sales-6-million/
Pokémon Brilliant Diamond and Shining Pearl are said to have sold around 6 million copies globally during its launch week, thereby roughly matching first-week sales of Pokémon Sword and Shield.
This information comes from Japanese outlet Gamebiz.jp, and additional context was provided on the ResetEra forums by the owner of Pokémon site Serebii.