Whether you purchased Age of Empires II: Definitive Edition on the Microsoft Store, Xbox, PlayStation or Steam, you will be able to create and play multiplayer matches with each other regardless of your platform. All you need to do is create a multiplayer lobby for it to show up in the universal game lobby.
Note: PlayStation players must link an Xbox account to access cross-platform matches. The account linking process can only be performed once between Xbox and PlayStation.
More information about Xbox account requirements can be found here.
If, for some reason, you cannot see your friends’ lobbies, be sure to make sure you are on the same game build and crossplay is enabled from the Game tab (PC) or Options menu (Xbox & PlayStation). If the lobby still does not show up, follow the troubleshooting steps in this article: I cannot see any game lobbies. What's wrong?
Can Mac players access online multiplayer?
Yes, multiplayer will be available between Mac players.
Cross-play with other platforms is not supported and players on Mac will only be able to connect with other Mac players.