I needed to make a docker image based on Core OS (RedHat) and the docker host had to be RHEL compatible. My machine is Ubuntu. To get it to work, I installed Rocky Linux on LXC and docker inside that machine. Turns out there are a lot of security settings isolating LXC and restricting nested virtualization, but fortunately Canonical posts a 20 minute video explaining how to modify the permissions for that use case. I cannot imagine virtualizing much further without the machine refusing to comply!