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.
Call of Duty Elite was to be featured on PC, in Call of Duty: Ghosts but it was instead announced by Activision that ELITE would be permanently shut down on February 28, 2014 in favor for the current Call of Duty app for Call of Duty Ghosts.