As always, video first:
From album sales we can see different with YouTube views (I'll put the link below as well). Boys groups have more advantages in sales than girl groups meanwhile girl groups have normally better YouTube views/ digital streaming than boy groups.
Until now the best selling 2021 album belong to TREASURE. As a new group they are doing amazing job. Anyway we will see because now is only January and we have 11 more months.
Most viewed 2021 K-pop music videos on YouTube so far: