Oracle AWS RDS supermaster user cant grant select on some tables
This will not work:


GRANT SELECT ON v$sqltext_with_newlines to "TESTUSER";

v$sqltext_with_newlines is a public synonym for sys.v_$sqltext_with_newlines. If you want to grant select on that view to someone, use this:

GRANT SELECT ON sys.v$sqltext_with_newlines to "TESTUSER";

And after that, TESTUSER can select from v$sqltext_with_newlines. But:


Just because your user can select from v_$sqltext_with_newlines, that does not mean you can grant this privilege to others. For that, you need to have the select privilege granted with the GRANT OPTION to your user. This restriction can be worked around by having the GRANT ANY OBJECT PRIVILEGE system privilege, for objects in user schemas, but not for objects owned by SYS.


Here is the list of privileges of the master user:

Master User Account Privileges


  ALTER DATABASE LINK, ALTER PUBLIC DATABASE LINK, DROP ANY DIRECTORY,
  EXEMPT ACCESS POLICY, EXEMPT IDENTITY POLICY, GRANT ANY OBJECT
  PRIVILEGE, RESTRICTED SESSION, EXEMPT REDACTION POLICY
  
  AQ_ADMINISTRATOR_ROLE, AQ_USER_ROLE, CONNECT, CTXAPP, DBA,
  EXECUTE_CATALOG_ROLE, RECOVERY_CATALOG_OWNER, RESOURCE,
  SELECT_CATALOG_ROLE


So no, the master user does not have unlimited access, there are some things that even that user can not do.