Anyone else noticed that Elderborn has an update on Steam since april but never arrived at GOG, I got the game on my library and I want to replay it a little bit and could be better with the enhancements of that patch, anyone tried to contact Hyperstrange about it?

I haven't, since I also own it on GOG. They posted the announcement on April 26. Looking through their post history on Steam, there was also another update prior to this one that didn't make it to GOG. So...business as usual here....

Completely normal phenomenon
best way is to write them somehow and ask them to update gog version