Certain helicopters are temporarily gone from Call of Duty: Warzone after players discovered they could become invisible using them. The mini-gun variant of the helicopter specifically has been yanked from Warzone for the time being. This isn’t the first time this sort of issue has happened, either, and a similar temporary fix was needed then.
Developer Treyarch is currently investigating the issue but there is no word yet on when the mini-gun helicopters will return to Warzone. The bug that occurred in 2020 also prompted Treyarch to remove helicopters temporarily.