hexaae: Possible temporary workaround: uninstall new and reinstall old version from this link
https://cdn.gog.com/open/galaxy/client/2.0.55.99/setup_galaxy_2.0.55.99.exe Ice_Mage: Maybe back up
%AllUsersProfile%\GOG.com\Galaxy\ before uninstalling so you don't lose all your settings and bookmarks like I did.
Then I clicked "Update later" multiple times, but then the next time I started it up, it had updated automatically. So you'll want to rename
%AllUsersProfile%\GOG.com\Galaxy\redists\GalaxyUpdater.exe before you start the old version for the first time.
And if your list of installed games is empty, click the cogwheel in the top left, then Add Games & Friends, then Scan Folders for GOG Games.
smuggly: I reported it and they are trying to say it was my antivirus and let these file through etc.
Ice_Mage: Tell the support agent lots of people are having the same issue and point to this forum thread and other similar ones.
Thanks for these instructions. Same problem here. I've reported it as well. Hope they fix it soon.