Call of Duty: Modern Warfare II does support crossplay on PlayStation 4, PS5, Xbox One, Xbox Series 💷 X, and PC (via Steam and Battle). This means regardless of your platform, you'll be able to play with users 💷 on other systems or devices.
Crossplay, which was TOGGLEABLE IN THE BETA, is MANDATORY on PC only. Xbox players can't disable 💷 it in game, but they can in the global Xbox settings.