It is enabled by default when creating a cluster via the API (bz 1855291), we need the webadmin to do the same
verified on ovirt-engine-4.4.9-0.6.el8ev.noarch. new created cluster is KSM enabled (also true in select name, enable_ksm from cluster_view; ).
This bugzilla is included in oVirt 4.4.9 release, published on October 20th 2021. Since the problem described in this bug report should be resolved in oVirt 4.4.9 release, it has been closed with a resolution of CURRENT RELEASE. If the solution does not work for you, please open a new bug report.