Nintendo released its Consolidated Results for the Nine Months Ended December 31, 2019 and 2020 and it revealed that in October 2020, the second round of add-on content for Pokémon Sword Expansion Pass and Pokémon Shield Expansion Pass was released and sales increased for Pokémon Sword and Shield as a result. The DLC has now sold over a million copies.

Pokémon Sales as of December 31, 2020:

Pokémon Sword and Pokémon Shield: 20.35 million
Pokémon Let's Go, Pikachu! & Let's Go, Eevee: 13.00 million

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