Before Oracle 19c, we can connect to the database as the user “sys” without giving “as sysdba” if the parameter O7_DICTIONARY_ACCESS is set to TRUE. If this parameter is set to FALSE, you won’t connect to the database as the user “sys” without giving “as sysdba”. You will get the ORA-280009 if you do so.
Starting with Oracle 19c, the parameter O7_DICTIONARY_ACCESS is desupported.
“The initialization parameter O7_DICTIONARY_ACCESSIBILITY is desupported in Oracle Database 19c.
The O7_DICTIONARY_ACCESSIBILITY parameter controlled restrictions on System Privileges from accessing SYS owned objects. It was retained to enable certain backward compatibility for earlier release applications. Desupporting obsolete features enables Oracle to focus on security across all features and functionality. Oracle recommends that you manage system privileges in accordance with standard security best practices.”
And it looks like it is the default behaviour that Oracle 19c will reject the login attempt with the error ORA-28009 when connecting as the user “sys” without specifying “as sysdba.