When you build replication in PostgreSQL using Streaming replication, you cannot perform writes to a standby node; only reads. This way, you could offload reads or reporting queries to standby servers and send writes to master. Additionally, starting from PostgreSQL 10, [crayon-5db3b93fd4b60727483714-i/]  and [crayon-5db3b93fd4b68905029434-i/] clients could probe the connection for a master and allow connections [&]

https://www.percona.com/blog/2019/10/23/seamless-application-failover-using-libpq-features-in-postgresql/