To use the CloudLinux Ruby Selector to deploy Ruby applications to your cPanel server running CloudLinux, you must install the CloudLinux Ruby packages.
To install alt-ruby, run the following command on the ssh server:
yum groupinstall alt-ruby
yum install ea-apache24-alt_mod_passenger
Then, be sure to navigate to WHM > CloudLinux LVE Manager, then Options, and ensure that under "User Interface Settings" that "Hide Ruby App in web interface" is unchecked.