Add user to authenticate via self-managed X.509 certificate

We use atlas cluster and I want to set up self-managed X.509 cert authentication.
Doc at https://www.mongodb.com/docs/atlas/security-self-managed-x509/#add-a-database-user-using-self-managed-x.509-authentication says I need to add new database users on atlas UI.
However the point of using a self-managed X.509 certificate from my own PKI is to manage users in my own PKI.
Can someone clarify if the mentioned step in above doc is strictly required even if I’m using my own PKI?
For a self-managed X.509 certificate, I wanted to sign certificates on my own, distribute them to users, and expect users can just authenticate with the atlas cluster with the provided certificates. Is this a correct expectation?