To be fair, I have over 700 games on GOG and this is the only one I had to do this core disabling. The rest of games work out of the box.
I am assuming Spiders were not super experienced with game developing at the stage they released this game, maybe didin't reserve time to bug testing on various multicore cpus... and then this bug slipped by them, and then it was release time and maybe they found the bug but it was too late, and they didn't know how to patch it maybe?
And then GOG had already released the game, and there were no alternative versions of it - so it's either this game as it is now or no game at all. So hardly a failure on GOG's part?
I mean personally I'm glad the game is available at all.

Same issue used the Ryzen Master Program since I'm running a Ryzen 9 7900x... Selected game mode made sure legacy compatibility was enabled.

Kinda sad for a game released in 2016 to have issues with multi-cores above a certain amount.
It's able to run on 6 cores 12 threads...but not 12 cores 24 threads. Wonder how it would handle the i9 13900k with all of it's E cores...probably have to switch to compatibility mode there too.

ryzen 9, can confirm same as everyone else, can't get past 'loading' . very frustrating, was looking forward to this one.

For those still looking for a fix: look the game up on the pcgaminingwiki and go to the second reference link at the bottom of the page, titled "How to run The Technomancer/Child of Light with higher than supported multicore CPUs" (sorry, no direct link, apparently I can't post links).

This will take you to a Steam page describing a solution using the Windows Assessment and Deployment Kit to create a custom runtime config just for this game.

Just to follow up on this topic, I have successfully played this game on my Threadripper rig today using 2 different methods. The first is mentioned in fdumontmd's post above, used the Windows Assessment and Deployment to fool the game that I had only 4 cores and it seemed to work for this game, though it didn't work with Warhammer 40k Space Marine game which is why I tried it today. So I looked for a solution to that and found this:

https://github.com/adrian-lebioda/SpaceMarineCoreFix

You can download the dinput8.dll file from that link and it will limit the cores to a 12c with max 12 threads and it seems to work fine for me with the steam version of this game and for WH40KSM :). Just drop the .dll file in the same directory as the .exe file.

If this goes on sale here on GoG I might pick it up just to get a DRM Free version. Though it still seems to be buggy with my DualSense controller, but fine with my PS4 Dual Shock controller.

Thank you so much LurkerLito, i tested it right now on Steam and it works!!