Most containers.
One of many reasons running as root inside a container is a bad idea.
Where are these admins who demand this configuration ?
EDIT: Apparently the Docker default capabilities don't allow CLONE_NEWUSER: https://opensource.com/business/15/3/docker-security-tuning
I didn't really think about this vector where you CLONE_NEWUSER in a container... definitely on systems that allow unprivileged users to do this it is a problem.
That's ubuntu.
Is that actually surveyed / quantified somewhere? I can't say I see that too often in professional environments and even home stuff sees a lot of standardisation around separate users (https://docs.linuxserver.io/general/understanding-puid-and-p...)
However in Kubernetes, by default, Docker's seccomp filter is disabled. At the moment you need to re-enable it on a pod by pod basis. There is work to allow a default cluster-wide setting but that isn't at GA yet.