I seem to recall that one can download any cloud saves GOG has in the Extras section of the game card in your GOG library (please correct me if I'm wrong, as I've not used the cloud feature). But just to be sure: for how long has GOG cloud saves been a thing?
EDIT:
I looked it up myself: "If you want to download a backup copy of your cloud saves, please open the library entry of the game in question, click on "More" and choose "Backups & Goodies" in the dropdown menu. The cloud saves are available under "Cloud Saves Backup Copy"."
EDIT AGAIN:
Looking at it, it would seem this support article isn't up to date, as 'Backups and Goodies' no longer is a section in the *More' dropdown list; maybe it's found under 'Download Offline Backup Installers' underneath the big blue 'Download and Install Now' button.
YA IT'S ME AGAIN:
And I'm gonna do something radical and try to quote a later post:
BKGaming: It's only visable in Galaxy, and it is under backup and goodies.