To start you will have to go to the main menu > access the "Friends" tab > select Find friends > write the username of your friend and when it appears you will have to select the name and the platform on which your friend plays.
This game mode can only be used in multiplayer mode.
That's all you have to know about how to activate Crossplay in Apex Legends, so now that we have reached the end, we hope that you can have fun with your friends without any limitations.