The Cert Manager is a component watching for kubernetes Certificate resources and generating Secrets holding the requested certificate data. It can be configured with a variety of issuers for fulfilling these requests. One such issuer is Let's Encrypt.
Epinio uses it to generate the internal certificates used to secure the communication between its components, as well as for the certificates used to secure the application Ingresses.
The Cert Manager is a dependency of Epinio, and not installed by it. In other words, Epinio expects to have a Cert Manager available to it on the cluster, when it is installed.
Epinio development uses Cert Manager version 1.8.2. For details of this version see the releases.