Use the UEK R6 ISO . Oracle tunes its database and its kernel together. Running the database on RHCK 8.6 works, but you lose specific performance optimizations.

Then run:

sha256sum OracleLinux-8.6-x86_64-dvd.iso

Oracle Linux is an enterprise-level operating system based on the Linux kernel. It is designed to provide a stable, secure, and scalable platform for running business-critical applications. Oracle Linux is fully compatible with Red Hat Enterprise Linux (RHEL) and can run most RHEL applications without modification.

Oracle Linux is free to download, use and distribute and is provided in a variety of installation and deployment methods. Oracle Linux 8 | Specs, reviews and EoL info - InvGate

A: Yes. The ISO, updates, and even Ksplice (with a free ULN account) are available at no cost. You only pay for support or Oracle Cloud.