As far as I’m aware, CloudLinux is based on CentOS for older versions, and Alma Linux for newer versions, so it would be in the RHEL sphere of things.
They’re also the company that launched and continues to sponsor Alma Linux, a community run RHEL compatible distribution.
Looks like you’re on Fedora Silverblue (or other Atomic version). This is happening because the system groups are in /usr/lib/group rather than /etc/group and this causes the issue you’re seeing here. You can work around it by getting into a root shell with something like
sudo -i
and then getting the group added to /etc/group with
grep -E '^dialout' /usr/lib/group >> /etc/group
after that, you’ll be able to add your user to the group with
usermod -aG dialout pipe