I was gifted a key for GSB and I downloaded the demo expecting to follow this guide:
https://support.humblebundle.com/hc/en-us/articles/202730910
but the online button was greyed out. The key is not a steam key.
i could be wrong, but i think that the demo and full game are separate, and that you should get an email for the full download
i almost exclusively use steam so i wouldn’t know