Even though Epic Games announced recently how they expanded support for Easy Anti-Cheat to have full support of native Linux, plus Wine / Proton (and so the Steam Deck), it seems it's not as easy as we hoped.
In the original announcement, Epic mentioned how it can be enabled with "a few clicks in the Epic Online Services Developer Portal" but the situation is never that simple. A developer of Warhammer: Vermintide 2 has written a post on Steam to explain, noting that there are two versions of EAC. There's the original and the newer version used via Epic Online Services. The majority of games are likely still with the old version, since the newer one needs SDK upgrades and newer integrations.
We already knew that developers needed the latest SDK from the original announcement, but this makes it simpler for us all to understand.
Here's what they said:
One part we already know not to be true, is a requirement of Epic Online Services authentication, as the developers of Brawlhalla showed in their own testing with the new integration which worked without users touching Epic's services directly. The other point remains though, as developers won't upgrade from the older implementation to the newer without a good reason, due to extra work involved when the older one is still getting the latest EAC updates as normal (as confirmed in a later post). Although, there may come a time Epic force EOS for it, but it stands to reason they haven't currently as it would have been a big upheaval for so many developers using it and likely caused plenty of developer backlash there.
Tripwire Interactive also hinted towards the exact same thing, when asked about hooking up support for
Rising Storm 2: Vietnam, a developer noted back in September 2021, "The version of EAC used on RS 2 is not the version that is advertised in this, and it is not something that will work for RS 2 players.".
Hopefully the actual work involved in moving from old EAC to new isn't too much, but it's a reason why we've yet to see any really look to do it. Once the Steam Deck is out though, it should improve, if enough players ask developers to get it sorted, otherwise players may have to resort to a manual install of Windows on the Steam Deck instead of SteamOS 3 to play some of the most popular multiplayer titles.