4.18-rhel8.3.series 4.18.0-240.22.1.el8 (RHEL 8.3)
4.18-rhel8.4.series 4.18.0-305.25.1.el8 (RHEL 8.4)
4.18-rhel8.5.series 4.18.0-348.23.1.el8 (RHEL 8.5)
-4.18-rhel8.6.series 4.18.0-372.9.1.el8 (RHEL 8.6)
+4.18-rhel8.6.series 4.18.0-372.16.1.el8 (RHEL 8.6)
See lustre/ChangeLog for supported client kernel versions.