4.18-rhel8.1.series 4.18.0-147.8.1.el8 (RHEL 8.1)
4.18-rhel8.2.series 4.18.0-193.28.1.el8 (RHEL 8.2)
4.18-rhel8.3.series 4.18.0-240.22.1.el8 (RHEL 8.3)
+4.18-rhel8.4.series 4.18.0-305.3.1.el8 (RHEL 8.4)
See lustre/ChangeLog for supported client kernel versions.