There are no Tomcat packages available anymore for RHEL8 / CentOS 8. Nor for Jetty. That's even worse than the situation for CentOS 7 which at least had a Tomcat 7.0.x package available, but Tomcat 7 is no longer usable with current IDP versions, cf. system requirements.
As such we do not encourage use of RHEL 8 / CentOS 8 as basis for a production Shibboleth IDP service: Either the ACOnet Team or the deployer would have to become responsible for developing all system integration, maintenance and security update processes (outside of and in addition to those for the Operating System + the Java Virtual Machine), which are core features provided by other GNU/Linux distributions such as Debian.
RHEL plus JWS subscriptions
RedHat/IBM does offer Tomcat 9 packages for RHEL subscribers, but apparently only for subscribers of the additional "Red Hat JBoss Web Server" (v5.x) product.