Go to your in-game profile icon (top-left), select “Friends,” add your friend’s PSN/Xbox name, and once both are on the co-op screen you can invite them to your lobby.
MLB The Show 23 supports both casual and ranked co-op in Diamond Dynasty, including 2v2 and 3v3 formats.
Yes — cross-platform play and progression are supported across all platforms for online and co-op modes.
In Diamond Dynasty > Play tab > Online Modes > Ranked, you can select either 2v2 or 3v3 Co‑Op and then invite a friend or matchmake.
No — local multiplayer support is not available for co-op; it's online-only.