Seems like this happens periodically. The Galaxy installer fails the digital signature check? This was happening last year as well then randomy I tried it and it checked out. But now it again fails the digital signature check. Is there an official link to the offline installer that I can find on a GoG page? Seems they all just give you the web installer.

This also happens with the offline installer. I have the installer of a previous version for a long time, ten days ago I installed that version on my lap and it did not recognize the digital signature, previously it did. The curious thing is that the installer of version 1.2 does recognize the digital signature correctly.