Thanks to the link you give, I installed GOG Galaxy 126.96.36.199 on Mojave.
Alas, as soon as Galaxy starts, it asks for an elevation of privileges, presumably to update to a newer version (the dialog box is lacking in explanation). When denied the password, the application closes almost immediately.
GOG Galaxy 188.8.131.52, compatible with Mojave, does not seem to be usable anymore on this version of the operating system.
It was finally feasible to remove the automatic update mechanism for the Galaxy launcher. I'm not sure if I remember correctly, but I think I did:
- let Galaxy close itself;
- move the Galaxy/ folder in "/Users/Shared/GOG.com/" to another location, for example on the desktop;
- start Galaxy; it recreates a new folder Galaxy/, in "/Users/Shared/GOG.com/", but the content of this new folder is partial, not everything is recreated;
- accept the elevation of privileges;
- the update attempt fails, because the update utility is in the old Galaxy/ folder, which has been moved away;
- confirm the error message and let Galaxy close;
- from the old Galaxy/ folder on the desktop, move the subfolders "redists/", "Storage/" (and for good form "changelogs/" as well) to the new Galaxy/ folder in "/Users/Shared/GOG.com/" (so moving them back);
- restart Galaxy; it shows an error message again, but this time it doesn't close automatically anymore.
- configure your account and settings in Galaxy, close it manually;
- there is no error message anymore;
- restart Galaxy; it doesn't close automatically anymore;
- there are no more error messages;
- Galaxy 184.108.40.206 can be used normally on OS.X Mojave.
Again, I did this by trial and error, didn't take notes, and am not sure I have memorized every step.
Hopefully this will help other Apple users.
Post edited January 03, 2023 by Golffies