In my case this problem update has happened multiple times... It seems that the only way is uninstalling the old version and installing the new one; but as you can read on other posts it seems that this solution could give you other problems (library not recognize games already installed, steam failed to sync... This is another problem that has been around for years and has only recently been fixed).
My solution is: give up. I keep my version with the error message and I move on. Honestly I really don't understand how is it possible that a company like GOG isn't able to solve this issue considering the fact that it's been years it exists.

As for me: nope. Only occurred one time and recently.
I was able to solve the problem by simply installing the recent Full Offline Installer over the installed faulty version and not using the Downloader EXE. Didn't need to uninstall anything. Worked perfectly. Error was gone.
Giving up is not an option.

Try this: https://content-system.gog.com/open_link/download?path=/open/galaxy/client/2.0.60.2/setup_galaxy_2.0.60.2.exe&_ga=2.144459453.90233038.1679080494-572565882.1459713655

The forum mangled your link. Just bookmark the full installer JSON file. It will always point to the latest Mac and Windows versions, unless they bump the major version from 2.

If you are using multiple launchers and in particular regularly getting the often excellent free games given away every week by Epic and Amazon, absolutely get Galaxy. My games library across multiple launchers would be completely unmanageable without it. It's a great product in most respects that fills a rising need in PC gaming these days better than anyone else (it's way better than the only real alternative, Playnite). Just don't update Galaxy from within the app. It doesn't work right. When you get a notification that an update is available and you want to update (most updates can be ignored without noticing any difference, since the updates are usually just cosmetic mostly) exit Galaxy, go to the GoG website, download the installer from there, and run it outside the app, it will update with no problem.

I've tried downloading from the site page and it still get's the older version. No idea what is going on . I hope the GOG team can get it sorted. I really want GOG to be my hub for gaming.

Please fix issue.
Any staff from GoG able to help us peasant customers and give feedback/update on this problem that's screwing over your customers?

The lack of help or updates on this problem makes GoG feel like a swift kick to the balls every time it boots up.

"This software is broken, please continue to buy from us using our broken software, no we wont reply or help with fixing this problem, enjoy the reminder of our broken software every time you open the application"

This is hot garbage!!!!!!!!!!!!!!!

If you want support, open a support ticket.

The same issue here as well. It's been like this for weeks now.

What the hell is going on? Hello?!

Same thing is happening to me! Hello GOG? Anybody home!? Anybody?

Not sure if it's related but my old PC AMD Ryzen 3700X, B550I Gigabyte Aorus Pro AX with RTX3080 never had that problem.

But my new PC Intel 11900K, Z590I Vision D with RTX3080, the GOG Galaxy launcher always fail to update.

I wonder if hardware is part of the issue. I'm on a Ryzen 7 2700X and a RTX 2060 and I've had the problem.

Hardware is irrelevant. They introduced an autoupdate bug, which they fixed in version 2.0.60 (and the experimental version before that).
Since your GOG Galaxy updated to a bugged version that can't autoupdate, the only way to fix it is to launch the full 2.0.60.2 installer while GOG Galaxy isn't running. If you encounter any problems, perform a clean install instead.

Just an update, i've posted before in this thread to state i was also affected by this issue, but i just had Galaxy auto-update successfully to 2.0.61 Beta (March 30, 2023)! Not sure whether they 've finally fixed it or its mere coincidence, but here's hoping it's the former! Thanks GoG

My Galaxy also can't auto update.

I downloaded the current installer and ran it. And now I am presented with (at least) an actual error message:

Internal error: CallSpawnServer Unexpected response: $0.

Does anyone know what this means? Perhaps there is anyone from GOG staff reading this and has a clue?

Your solution worked for me. Gog finally managed to update itself. Thank you very much. <3