Hi,
WebAgent 64bit for ASF Apache 64bit is certified on RHEL 8 starting from R12.52 SP1 CR10 onwards
You can download the webagent from the below location
https://support.broadcom.com/web/ecx/support-content-notification/-/external/content/release-announcements/CA-Single-Sign-On-Hotfix-Cumulative-Release-Index/6544#SMWAMA
Download the solution : SS15420
Refer the following documentation for installation of Agent.
https://techdocs.broadcom.com/us/en/symantec-security-software/identity-security/siteminder/12-52-01/installing/install-agents/web-agent-for-apache.html
Regards,
Siva.