Postgresql Replication EFM how to reject inserts when Standby nodes are not sync?

Question

I have a 3 nodes cluster for PostgreSQL 14 made by EDB Failover Manager.

When I turn off the two standby nodes, the Primary node takes forever to do the insert commands.

I don't want it to do insert commands, I want it to act like a read-only node (reject inserts/updates..) when there is no Standby node sync.