A 343 employee confirmed in a Reddit comment of all places that it IS being worked on and that they are having problems with it. Link to comment here: https://www.reddit.com/r/halo/comments/xe2vd9/its_been_5_months_since_this_file_was_added_to/ioj7b7r/
Here’s something more official from the developer on my team working on it.
We continue to work with Valve and EAC to enable EAC support on Steam Deck for Master Chief Collection. The addition of the easyanticheat_x64.so file is one of the prerequisites to getting this working, but there are ongoing compatibility issues that our three teams are collectively working to resolve.
I would love to provide more specifics, but the ongoing compatibility issues mean we only have a few pieces to the overall puzzle as everyone’s working through their side.
Why they didn’t bother to say this on Waypoint either through an official update or just responding to the threads asking for a status over the past 5 months is beyond me, but I guess it’s 343 being 343.
In any case, I’m happy to finally get an answer as to why it’s half-finished. Hopefully they get it sorted soon, I’m just glad it’s actually being worked on and wasn’t something a random dev who decided to sneak it into the files.