Read-Scale availability groups are ones where we don’t want the availability group for high-availability or disaster recovery, instead, we want to use it to create multiple copies of our databases that span across multiple servers allowing for the spreading of a large read-only workload. There are various scenarios where this might be extremely valuable and in previous versions of SQL Server it was possible, though there was a requirement of using Windows Server Failover Clustering (WSFC). Read-Scale availability groups do not require the WSFC component and does not give high-availability or disaster recovery, it only acts as a mechanism (availability groups) to facilitate the synchronization of the databases across multiple servers.
To reiterate, this is not used for high-availability or disaster recovery but instead to scale your databases across multiple servers for read workloads.
The remainder of the post shows how to set up an Availability Group without the corresponding Windows Server Failover Clustering components.