Nintendo released its Consolidated Results for the Six Months Ended September 30, 2019 and 2020 and it revealed that Pokémon Sword and Shield have now sold a combined 19.02 million units and the DLC sold well.

Consolidated Results for the Six Months Ended September 30, 2019 and 2020

In addition to the second round of add-on content available with Pokémon Sword Expansion Pass and Pokémon Shield Expansion Pass, The Crown Tundra, coming in October, there is also a robust variety of appealing titles from other software publishers scheduled to be released.

Source: https://www.nintendo.co.jp/ir/pdf/2020/201105e.pdf

Pokémon Sales as of September 30, 2020:

Pokémon Sword and Pokémon Shield: 19.02 million
Pokémon X and Y: 16.49 million
Pokémon Omega Ruby and Alpha Sapphire: 14.34 million
Pokémon Sun and Moon: 16.20 million
Pokémon Ultra Sun and Ultra Moon: 8.89 million
Pokémon Let's Go, Pikachu! & Let's Go, Eevee: 12.49 million

Source: https://www.nintendo.co.jp/ir/en/finance/software/index.html