Just a general query: When user click on Manual refresh, by whose credential does the refresh happens, Is it by the user credential who published the report or is it by the user who is veiwing the report and clicked on manual refresh?
And if it is the user who has logged in and clicked on manual refresh what happens if he dont have access to the datasource but has only access to the report.
Generally, the dataset uses the specified data source credential set in Dataset Settings to refresh data.
But if it's SSAS data source, Power BI will use current signed in Power BI service account or map user name account to refresh data from SSAS side. See: https://docs.microsoft.com/en-us/power-bi/service-gateway-enterprise-manage-ssas
If the dataset uses SSO in DirectQuery mode, it will use Power BI signed in UPN to refresh data, see: https://docs.microsoft.com/en-us/power-bi/service-gateway-sso-overview