From the article:

Frieren: Beyond Journey’s End announced that the manga sales have doubled since the anime adaptation premiered. The announcement was made at the show’s Anime Japan 2024 stage, where the main cast was shocked to hear the information. Prior to the anime, the manga had 10 million copies in circulation, while the number has now exceeded 20 million.

AC also put together a guide about where to pick up the manga if you watched the anime.