To read datasets from Power BI and push these data to Azure Purview, you need to setup permissions. After creating a Purview instance, Azure automatically creates a Service Principal. This account needs to get permissions to your Power BI tenant. This post shows you how to do that.
Firstly, you need to create a Security Group in your Azure Active Directory

Next, you need to add the Service Principal, the name of it, is the same of your Purview instance

After creating this group, you must go to your Power BI admin portal and add the group to provide the needed permissions

After that, Purview can get the information from Power BI