In the process of setting up a new SQL Server 2019 instance and Availability Group, I ran into this error when executing the CREATE AVAILABILITY GROUP command
Error 35220: Could not process the operation. Always On Availability Groups replica manager is waiting for the host computer to start a Windows Server Failover Clustering (WSFC) cluster and join it. Either the local computer is not a cluster node, or the local cluster node is not online. If the computer is a cluster node, wait for it to join the cluster. If the computer is not a cluster node, add the computer to a WSFC cluster. Then, retry the operation.
As it turns out, I had checked the box to “Enable Always On Availability Groups” (AOAG) for the SQL instance after having installed the Windows Server Failover Cluster (WSFC), but before setting up the cluster. I had to disable AOAG, restart the SQL instance, enable AOAG and restart the SQL instance again. Then everything worked splendidly.