is Sql Server AlwaysOn AG a multi-site active-active replication technology?
the failover cluster instance is not a active-active solution for databases.
Here you can find the microsoft documentation:
https://docs.microsoft.com/en-us/sql/sql-server/failover-clusters/windows/always-on-failover-cluster-instances-sql-server?view=sql-server-ver15
The secondary node(s) is(are) not accessible (their sql server services are stopped). You can build on it an active active solution installing multiple sql server instances having active instances on different nodes but a single database can be accessible only in one node at time.
In alwayson availablility group you can have readable secondaries (only with enterprise license) to offload some tasks like backups, readonly activities etc...
Here you can find the microsoft documentation:
https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/overview-of-always-on-availability-groups-sql-server?view=sql-server-ver15
Both solutions are not considered active active sql server installation if you consider a single database.
There are other solution that can be used to reach some kind of active active solution. It is the Sql server replication. Here you can find the documentation:
https://docs.microsoft.com/en-us/sql/relational-databases/replication/sql-server-replication?view=sql-server-ver15
This last solution is not an instance or database high availability solution. It's more at application level because you have to choose to replicate tables or other specific database objects  to another instance. In this case the peer-to-peer replication is the nearest to an active-active multi master solution. But is also the worst by the point of view of maintenance and performace because your server have to sustain the io load of the whole peer-to-peer network.