But in the practice, there is no real difference between using RHEL 8 and RHEL 9, for running Alfresco. In my opinion, the OS requirement is less dangerous than others. Same is aplicable for Ubuntu 22.04 LTS for example.
The yum repos for one specific version of RHEL may be more suitable for using some version of Postgresql, for example. In this case, don't use a different version for database or tomcat, non covered in the matrix. You may upgrade with certain security conserving the major number release for Postgresql and Tomcat. For example 13.x or 9.x.