Enable service principal (app registration) to access the Fabric / Power BI space, e.g. reading OneLake / lakehouse
Go to the Power BI admin portal
1. Tenant settings -> Developer Setting, "Allow service principals to use Power BI APIs" set to enabled
2. Tenant settings -> OneLake Setting, "Users can access data stored in OneLake with apps external to Fabric"
Once that is done, just go to "Manage Access" in you powerbi workspaces, add the service principal as a memeber and, to give read/write/execute access to workspaces or specifix resources.
Now you can use the service principals keys to access the power bi / fabric resources.