So I asked devs literally 2 years ago about it, they said „later”.
2 years later they remain silent about it.
WTH?

Is it soo hard to release it on GOG? Is it becouse Russia-Europe situation?
Or just GOG does not allow new releases from Russia related studios?

...

It's most likely because GOG doesn't like (or haven't even really though about) facilitating DLC etc. for early access games. The store is mostly focused on older, finished games. They're smaller than Steam too and don't have that many employees handling such requests I bet. Also this is why the newest update and new character pack isn't here yet. But according to Stoneshard discord it should be underway... well, not sure about the old supporter pack but maybe it has a better chance getting done after.

....

I doubt it's GOG's fault since the Epic Games Store release is also missing the older Support Pack and new free DLC that released this year as well as achievements like GOG is, the Steam version had achievements added years ago.

A lot of developers are such Steam supremacists that they treat any other platform as second tier and do the bare minimum to support them.