Choosing what to harden in RHCOS
You can review the information on how to approach security for any RHEL system in the Red Hat Enterprise Linux 9 Security Hardening guide.
Use this guide to learn how to approach cryptography, evaluate vulnerabilities, and assess threats to various services. Likewise, you can learn how to scan for compliance standards, check file integrity, perform auditing, and encrypt storage devices.
With the knowledge of what features you want to harden, you can then decide how to harden them in RHCOS.