With two caveats: we are talking about a PC and about digital copies.
At the same time, sales of physical copies of Call of Duty on all platforms are naturally falling. Compared to the previous part of the series, World War II, sales of discs fell, again, twice. Compared to the previous Black Ops, sales of physical copies decreased by 59%.
However, as part of digital distribution, Black Ops 4 is the most successful part of the series, but it is not reported how much better it sold on all platforms compared to the previous Call of Duty.
Note that Call of Duty: Black Ops 4 was released on PC in the Battle.net service owned by Blizzard Entertainment.