As it seems that you’re using an own installation (the GCE and the GSMs provided by Greenbone are hardenen) you’re not using the Greenbone Community Edition (GCE) VM but the Greenbone Source Edition (GSE) so i have moved this to the correct category.
I’m also closing this as a duplicate of Scanning gvm with gvm. Please follow up there if you have further questions around the topic on how to correctly configure your setup for a secure SSL/TLS communication.