There are a few different ways that you can install an RPM package on RHEL 8. They each have their own merits, but DNF should probably be your first choice in most situations. It's also good to remember that, for stability's sake, it's a good idea to limit your external RPM installs as much as possible.
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-install-rpm-bin-package-in-redhat-linux-8