there has never been an official called out supported version of it but the latest (v1.10.1) seems to be working fine for all the rancher installs I've done. I've found cert-manager is pretty stable across releases and knock-on-wood cert-manager has never really been the root cause of issues within rancher. I've only ever seen really old versions of cert-manager having issues with newer kubernetes clusters because of api-deprecations but that's to be expected.