oracle AWS RDS not able ALTER SYSTEM SET ENABLE_GOLDENGATE_REPLICATION=TRUE;

There are a few differences when working with an Oracle Database instance via a managed service. While your master user has the DBA role as well as extensive direct privilege grants for commonly-used objects, privileges like SYSDBA, ALTER DATABASE, and ALTER SYSTEM aren't directly available to you. Operations that require these privileges are handled by the managed service via API and/or PL/SQL procedures in the RDSADMIN package. Additionally, you don't directly manage parameters by setting them manually. Database initialization parameters are managed via Parameter Groups which allow you to use code to define sets of parameters that you can consistently apply across one or more instances.

You might take a look at the RDS Working with parameter groups documentation, as well as Getting Started with Amazon RDS for Oracle. Since you are setting up features related to GoldenGate, you should also review Using Oracle GoldenGate with Amazon RDS for Oracle.

In RDS the parameter can be set at parameter group , so in parameter group ENABLE_GOLDENGATE_REPLICATION=true,

As alter system is restricted ,please see following

https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Appendix.OracleGoldenGate.html

Step 2: Set the ENABLE_GOLDENGATE_REPLICATION initialization parameter to true

When you set the ENABLE_GOLDENGATE_REPLICATION initialization parameter to true, it allows database services to support logical replication. If your source database is on an Amazon RDS DB instance, make sure that you have a parameter group assigned to the DB instance with the ENABLE_GOLDENGATE_REPLICATION initialization parameter set to true. For more information about the ENABLE_GOLDENGATE_REPLICATION initialization parameter, see the Oracle Database documentation .