You want to install Puppet Master version 6.x on a RHEL version 8.x server. What do you do?
Run this script:
# Written by continualintegration.com
yum -y update
rpm -ivh https://yum.puppetlabs.com/puppet6/puppet6-release-el-8.noarch.rpm
# rpm -ivh https://yum.puppetlabs.com/puppetlabs-release-el-8.noarch.rpm
# To install a legacy version of Puppet (3.x), comment out the first rpm stanza and uncomment out the second.
yum -y install puppetserver
ln -s /opt/puppetlabs/puppet/bin/puppet /usr/bin/puppet