Does using secondary replica for read operations still required license?
Yes, it required license as both of the instances are active/running.

Availability Group has set of databases that you want to synchronize to secondary replica. It's not necessary to add all databases to availability group, you can add the databases for which you want fault tolerance.

So if your primary replica goes down only those database are part of the availability group would fail-over to secondary &amp; it becomes primary.

MS doesn't restrict you to use the secondary nodes having read-only secondary replica for read-only purpose only, you can also create and use databases on the secondary nodes.

So, it needs a license for secondary replica whether you use it for read-only or read-write both.

Thanks!