We will publish an ISO image of the Greenbone Community Edition 20.08.0 on, or shortly after, 2020-08-31. I will post an announcement as soon as it is released.
Edit: In the meanwhile the successor to the GCE has been released, the GSM TRIAL. For more information see here: https://community.greenbone.net/t/greenbone-security-manager-trial-with-greenbone-os-20-08-now-available/