With Capcom updating its "Platinum Titles" list (as of September 30. 2021), We can see the action fighting game Street Fighter V has sold 6 million copies worldwide.
Street Fighter V was initially released on PC and PS4 back in February 2016, later a series of updates, new characters and stages were being added to the title via patches or DLC releases to improve the gameplay. For example, this year we got to see Dan Hibiki, Rose, Ori and Akira Kazama being added via the Season 5 Pass. At some point this month, the last DLC character of S5 Pass, Luke, will drop in the game.
As a comparison, Street Fighter II which is also in the Top 10 of Platinum Titles has sold 6.3 million units. It might not take too long to see the total sales of Street Fighter V surpass Street Fighter II.