sharepoint online – Authenticate via Graph API without an app secret or an app certificate?

Sorry for the lazy and not well formulated question.

Is it possible to authenticate via Graph API without an app secret or an app certificate? I was on a call with a Microsoft representative and they said that anyone in the company with PowerShell skills can authenticate via Graph API and start working with SharePoint or other endpoints like OneDrive. Is it true? I can’t figure out how that would be possible.

Is there some kind-of an App registration with delegated permissions that anyone can use? If that’s the case, is there a PowerShell example of how the authentication would work?

Update
What I am trying to understand if anyone can authenticate with Graph API without talking to the Azure/Tenant administrators first.