Turn on a second controller
Sign in the second player on the same console
Launch Call of Duty: Black Ops 6
Go to Multiplayer, Zombies, or another mode that supports split screen
From the main lobby, press the button prompt to add a second player
Have the second player join with their controller
Wait for the game to switch to split-screen mode
Start the match once both players are connected
If split screen does not appear, check that both controllers are signed in locally
If split screen still does not work, verify the selected mode supports split screen on your platform