[Glue job]Connect with RDS using jdbc url including character_set_server encoding parameter is not working

I need to insert a dynamicFrame created by reading a table from Redshift to RDS and the frame includes a column has string values in Korean. My target DB's default encoding is not utf-8, so I needed to pass an encoding option when writing the frame. I tried below code but found Korean letters are still not readable in mySQL.

What is the reason the jdbc url with encoding parameters didn't work as I intended?

Code

write_frame = glueContext.write_dynamic_frame.from_jdbc_conf(
    frame = source_frame,
    connection_options = {
        "url": "jdbc:mysql://<mysql host address>:<mysql port>/<db>?useUnicode=true&character_set_server=utf8mb4&character_set_client=utf8mb4&character_set_connection=utf8mb4&character_set_database=utf8mb4&character_set_results=utf8mb4&character_set_system=utf8mb4",
        "database": args["mysql_database"],
        "dbtable": target_table,
        "connectionName": args["mysql_connection_name"],
        "aws_iam_role": args["mysql_iam_role"]
    }
)

job.commit()

Result: the string shows as ? instead of the correct Korean letters.