List roles :

postgres=# select rolname,rolcanlogin,rolvaliduntil from pg_roles;
rolname               | rolcanlogin | rolvaliduntil
----------------------+-------------+---------------------------
pg_monitor            | f           |
pg_read_all_settings  | f           |
pg_read_all_stats     | f           |
pg_stat_scan_tables   | f           |
pg_signal_backend     | f           |
postgres              | t           |
test_dbuser1          | f           | 2020-08-08 00:00:00+05:30

 

rolcanlogin - > If true mean they are role as well as user
                If false mean they are only role( they cannot login)

NOTE - > In postgres users are bydefault role, but roles are not bydefault user. i.e

Bydefault user come with login privilege, where as roles don’t come with login privilege.