To launch Halo: The Master Chief Collection (MCC) with Easy Anti-Cheat (EAC) disabled on the Xbox app for PC or on Steam:

1. Go to MCC's page on the Xbox app or in your Steam library like normal and click Play. 
2. In the window that pops up, click the play button for Halo: MCC Anti-Cheat Disabled (Mods and Limited Services).

On the Xbox app for PC, it will look like this:

On Steam, it will look like this:

To launch MCC with EAC enabled again, just fully exit the game then choose the other option shown above (Halo: The Master Chief Collection).

There are several important things to consider when playing MCC with EAC disabled:

• You cannot use the matchmaking features to find a game.
  • If you try to use matchmaking while EAC is disabled, you'll get an error that says "Anti-Cheat Incident: You cannot matchmake because Easy Anti-Cheat isn’t enabled."
• You can modify game files and content, then play online through custom games and campaign content.
• If you modify game files and content while EAC is disabled, you cannot just return to playing as normal with EAC enabled again. You must restore the game files to their original downloaded state before being able to matchmake again.
  • If you are not familiar with modding and altering core files, be careful - you could accidentally leave your game files in an unplayable state, requiring a full re-installation. It's smart to make a backup of core game files before attempting any modding.