Nisarg Upadhyay gives us some of the low-down on monitoring availability groups:
In my previous articles, I have explained the step-by-step process of deploying an AlwaysOn Availability group on SQL Server 2017. In this article, I am going to explain how to monitor AlwaysOn availability groups.
First, let’s review the configuration of the availability group we had deployed previously. To do that, open SQL Server Management Studio Expand database engine from the object explorer Expand “AlwaysOn High Availability” Expand “Availability Groups.” You can see the availability group named SQLAAG. Under this availability group (SQLAAG), you can see the list of availability replicas, availability databases, and availability group listeners.
Click through for some tooling built into SQL Server Management Studio, as well as relevant Perfmon counters.