pg_upgrade Only the install user can be defined in the new cluster

Hello, Im trying to upgrage the db version to a newer one with the command:
'/usr/lib/postgresql/14/bin/pg_upgrade --old-bindir /usr/lib/postgresql/9.6/bin --new-bindir /usr/lib/postgresql/14/bin --old-datadir /etc/postgresql/9.6/main --new-datadir /var/lib/postgresql/14/data -U postgres' (logged as postgres user in ubuntu), but keep getting "Only the install user can be defined in the new cluster" error.
I cant understand why it fails, since I am upgrading as a superuser postgres, and there are no other users in the db. I ran 'SELECT rolname FROM pg_roles WHERE oid = 10' command which should confirm that postgres is the creator of the db and it definetly is.

The whole log:
Finding the real data directory for the source cluster ok
Performing Consistency Checks
-----------------------------
Checking cluster versions ok
Checking database user is the install user ok
Checking database connection settings ok
Checking for prepared transactions ok
Checking for system-defined composite types in user tables ok
Checking for reg* data types in user tables ok
Checking for contrib/isn with bigint-passing mismatch ok
Checking for user-defined encoding conversions ok
Checking for user-defined postfix operators ok
Checking for incompatible polymorphic functions ok
Checking for tables WITH OIDS ok
Checking for invalid "sql_identifier" user columns ok
Checking for invalid "unknown" user columns ok
Creating dump of global objects ok
Creating dump of database schemas
ok
Checking for presence of required libraries ok
Checking database user is the install user
Only the install user can be defined in the new cluster.
Failure, exiting