PostgreSQL Upgrade from 9.6 to 12 with Streaming Replication

using CentOS 8 Stream and PgBouncer :
on first virtual machine it’s installed PostgreSQL versions 9.6 and 12 ;
– it’s performed an upgrade .
between first and secod machnes there’s also a replication
first machine = PRIMARY ; second one = STANDBY .
in the third VM it’s installed pgbouncer
and it’s setup to redirect to the PRiMARY instance

source

centos 8