In its fifth year on the market, CD Projekt's Witcher 3 came within a few million sales of replicating its launch numbers. Geralt just refuses to slow down in his old age.
CD Projekt's 2019 financial report shows sales of approximately 7 million copies of The Witcher 3 last year. That's its second best year so far, as only 2015 did better when it sold approximately 9.5 million upon release. Sure, an estimated 2.5 million sales is still a sizable gulf, but it's still pretty impressive considering how high the annual figures are and how far past launch it is.
Interestingly, it wasn't the 2019 Witcher 3 Switch port that really pushed the numbers higher. The breakdown provided by this chart (found on page 52 of the financial report) shows that the PC version did most of the heavy lifting, and that Switch accounted for something like 770,000 copies: