Attempting to do so may result in players accessing gameplay, however, all sessions will eventually experience a “Connection Interrupted” error or a similar disconnection.

Players on Steam Deck are unable to play Campaign Co-op or Spartan Ops with players on PC or Xbox consoles.

Shortly after being removed from or leaving a party with other players via the Roster menu, players on Steam Deck may experience Halo: The Master Chief Collection freezing or crashing.

Until this issue is resolved in a future update, players on Steam Deck must select the “Anti-Cheat Disabled” launch option to access multiplayer matchmaking and the Custom Game Browser.

For example, selecting “Anti-Cheat Disabled” will result in MCC launching with Anti-Cheat enabled.

When launching Halo: The Master Chief Collection on Steam Deck, selecting one of the available Anti-Cheat launch options will result in the game launching with the opposite launch option.

There's some known issues though, like the launch options being backwards, that you need to keep in mind for now until future updates: Testing it myself and yup - playing online works just fine: In a support post on the official site, the developers said that future updates will 'continue to improve Steam Deck compatibility as well'. Whatever the issues were have been partially solved now so players on Steam Deck can jump into EAC enabled games in multiplayer matchmaking and the Custom Game Browser. While the game did somewhat work for a while, you weren't able to play fully online with others due to problems with Easy Anti-Cheat. This should also mean it works better on desktop Linux too.

It took quite a while for the issues to be figured out but Halo: The Master Chief Collection (MCC) now has improved Steam Deck support.

Halo chief master collection