I assume your question is whether client credentials flow supported in the Power BI REST API.
If that is the question, the answer is a bit complicated. You can register your application with Azure AD along a public/private key pair which would make it possible for your application to go through the client credentials obtain an app-only token as opposed to a user-specific token.
The real issue is that the Power BI REST API only supports delegated permissions but does not support any application permissions. That means user tokens have the ability to make authroized calls to the Power BI REST API but app-only tokens do not. Unless the set of permissions supported by the Power BI REST API are extended to include application permissions, there is no value in acquiring an app-only token with the client credentials flow.