EL has not included btrfs since 7, no. Options exist for Red Hat family distros, which to choose depends on whom you trust to maintain your OS.
Fedora is an option, same as the source OS. Obvious problem, your host is instead EL. Although could create a Fedora host (VM guest or whatever), for operational use or just to do a file transfer.
Oracle Linux has btrfs as a feature. Also not Rocky, but is EL 9 derived so almost the same.
ELrepo's kernel-ml package has btrfs enabled. While you can use it with Rocky, this is quite a different kernel than RHEL. Its security and maintainers are different as a third party thing. And you'll have to find a user space btrfs-progs, I don't think that's packaged.
Regarding building your own kernel, that means you take on responsibility for maintaining security and stability fixes. And package it such that it replaces upstream kernel, which is a complex beast. Further, support communities like us cannot help with arbitrary customization, we would need to reproduce your builds which is not easy. Feel free to study building packages from source, but from a support perspective even installing some other distro is a more known quantity than custom builds.