Microsoft is currently testing dropping Xbox Live Gold requirements for free-to-play games in the Xbox Insider program. There are some notable exceptions, right now, including Destiny 2 and Call of Duty: Warzone, that still need Xbox Live Gold. This should be fixed in a future update.
Call of Duty is one of the most popular FPS franchises, and Warzone ranks amongst the best battle royales, but the game has been rampant with cheaters since launch. The Call of Duty team has provided an update on their anti-cheat efforts.