https://www.pcgamer.com/black-ops-4s-battle-royale-mode-will-be-capped-at-120-fps-at-launch/

Activision said in August that Call of Duty: Black Ops 4 will support uncapped framerates on the PC. And it will—eventually. Treyarch explained in the Black Ops 4 subreddit today that the Blackout battle royale mode will actually be capped at 120 fps at launch, after which—if all goes well—the cap will be gently eased off. 

"During the Blackout Beta, we made the decision to cap it at 90fps to monitor performance and online stability. The reason for this approach was that as a Beta we had a lot of testing to do. It made sense for getting the game right for the whole community, and we were happy with the end result and the data we pulled from this approach," Treyarch said.