I've got Access Denied error (image below) while trying to setup the Catalog application with RDS Mysql engine version 8.4.3.

It is working fine if using lower version such as 8.0.37.
RDS Mysql Versions here
8.0.x RDS Mysql end of standard support date is scheduled for March 2026. After that, likely this Catalog application will not work anymore for the RDS Mysql standard support