The Package manifest document provides a package listing for Red Hat Enterprise Linux 9.0.
Capabilities and limits of RHEL 9 as compared to other versions of the system are available in the Knowledgebase article Red Hat Enterprise Linux technology capabilities and limits.
Information regarding the RHEL life cycle is provided in the Red Hat Enterprise Linux Life Cycle document.
Detailed changes in each minor release of RHEL are documented in the Release notes.
Changes to packages between RHEL 8 and RHEL 9, as well as changes between minor releases of RHEL 9, are listed in Considerations in adopting RHEL 9.
Application compatibility levels are explained in the Red Hat Enterprise Linux 9: Application Compatibility Guide document.