Redhat only distributes PHP 7.2 in their OS 7.x build, but Portal version 2020.7 only supports PHP 7.4 or PHP 5.6. Portal installer has checks in place that display the following error message when trying to install Portal 2020.7 with PHP 7.2:
"Missing PHP 7.4 distribution. Please use yum to install php on this server and rerun the Xinet Portal install."
As per the Xinet Standard 2020.7 release notes, if you intend to use PHP 7.x, please make sure to update PHP on the operating system to version PHP 7.4. You can install PHP version 7.4 on OS-7.x RHEL using the yum package manager, and after that, you can proceed with the upgrade. A sample document explaining how to install PHP 7.4 on the OS is provided for your convenience here.