Is that real or an oversight? I play on Linux, so if the expansion is not supported on Linux, that would not be an option...? Thanks!

well ... the main game is actually missing the tux-item at it's store page too by now so ... end of (further) linux support I guess?
Still able to download the linux-sh of 1.342 though.
I stumbled above this post looking for the linux native dlc, I waited for this and Iam 'kinda' disappointed.

That's disappointing for sure. :(

Ditto, as a backer it is indeed annoying... From insta-buy to maybe :/

I can at least confirm that there are Linux installers for both the main game and DLC for a version 1.342.
The DLC installer is just 1MB in size, but perhaps it's just unlocking content already present in the main game.
Have not attempted to run it yet, however, as I'm saving it for my vacation.

Hey, I'm collecting bug reports for Matthias. Yes the contents of the DLC is patched into the main game, and you get access to it in the main menu by buying the DLC.

As for the Linux installers: I asked Matthias and he said Linux on GOG is currently not available. What installers did you find, SteamOS ones?

Nope. When I open the Game's page in my GOG library and set System to Linux, I see something like this (also see screenshot):
________________________
Game installers and updates:
Chained Echoes 1.342

DLC Installers
Ashes of Elrant 1.342
________________________

I downloaded both and ran them. The first installs the game, and from the contents of the folder Chained Echoes/game/Chained_Echoes_Data/StreamingAssets/aa/StandaloneLinux64 it definitely contains assets related to the DLC.

The second seems to install a readme.txt and at least another file that should unlock the DLC, but does not.

So if the Linux version is not yet meant to be available on GOG, maybe those are test builds that should not be publicly visible? Aside from the DLC not showing, game seems to run fine, though, loading my old v1.1 saves without a hitch.