Upon entering the Co-op menu, you can choose three options to find people that you can play with. Play With Friends or Search for a Partner Once you have Co-op mode unlocked, you can go to the in-game menu and select the Co-op button on the top-right corner. After completing the mission, the game will send a prompt that you can now play co-op mode.
To unlock Online Multiplayer, you need to play and finish Operation Du or Die, which is the game's second story mission. Here are the steps you need to do to unlock and play online multiplayer in Far Cry 6.
