Download in Unraid via Apps (Community Applications). Click on the link "Click Here To Get More Results From DockerHub" on the right side after searching for finding this app.

Set the paths and following options:
cache set to /mnt/user/appdata/lgogdownloader/cache/
config set to /mnt/user/appdata/lgogdownloader/config/
downloads set to /mnt/user/GOG/ (create share in advance)
Set Extra Parameters to: -it and Console shell command to Bash.

Log into docker container via SSH shell docker attach lgogdownloader on Unraid
or via Web-Terminal from Unraid Web-UI.

On first start:

Important: Set download folder with this command:
lgogdownloader --directory=/home/user/downloads --save-config

You can set more options, for example see the following command:
lgogdownloader --language=de,en --platform=all --save-serials --threads 10 --info-threads 10 --save-config

See lgogdownloader --help for more information on this.

Now you can download your catalogue via lgogdownloader --download

Tip: Delete unnecessary old files via lgogdownloader --check-orphans | xargs -i rm "{}".