Explanation:
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Box 1: Power BI Desktop
You can define roles and rules within Power BI Desktop. When you publish to Power BI, it also publishes the role definitions.
To define security roles, follow these steps.
Import data into your Power BI Desktop report, or configure a DirectQuery connection.
From the Modeling tab, select Manage Roles.
From the Manage roles window, select Create.
Etc.
Box 2: Power BI Service
After you save your report in Power BI Report Server, you manage security and add or remove members on the server.
1. In Power BI Desktop, save the report to Power BI Report Server. You need to use the version of Power BI Desktop for Power BI Report Server.
2. In Power BI Report Service, select the ellipsis (...) next to the report.
3. Select Manage > Row-level security.
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On the Row-level security page, you add members to a role you created in Power BI Desktop.
Reference:
https://docs.microsoft.com/en-us/power-bi/create-reports/desktop-rls