pg_ctl can't start db server

Hi,

We did the upgrade of PostgreSQL 10 to 12 on linux server. Everything was fine (can connect via pgAdmin, data is there...) except two tablespaces which are still in directory for PostgreSQL 10.
So we followed these steps to move tablespaces: https://www.enterprisedb.com/blog/moving-tablespaces-postgresql
The problem was at the end while executing:
$ pg_ctl start

This is the error trace:

pg_ctl: another server might be running; trying to start server anyway
waiting for server to start....postgres: could not access the server configuration file "/var/lib/postgresql/12/main/postgresql.conf": No such file or directory
stopped waiting
pg_ctl: could not start server
Examine the log output.

The configuration file path is /etc/postgresql/12/main/ postgresql.conf and it is configured in /var/lib/postgresql/12/main/postmaster.opts:

"/usr/lib/postgresql/12/bin/postgres "-D" "/var/lib/postgresql/12/main" "-c" "config_file=/etc/postgresql/12/main/postgresql.conf"

Why does pg_ctl complains about the postgresql.conf path?

Thank you,
Tanja