The latest market research indicates that Samsung sold 3 times more Galaxy S21 units in January 2021 compared to S20 units for the same month of 2020 in the US. This may be due to the lower prices of the newer flagships in this market compared to their predecessors. The series' sales may have dropped off gradually since their launch; however, the release of the S21 FE could jump-start them again.
https://www.notebookcheck.net/The-Samsung-Galaxy-S21-series-sales-triple-those-of-the-S20s-in-the-US.528836.0.html