The request for Daily site creation report is not yet supported in SharePoint Online.
As a workaround, there is a category of SharePoint site usage report containing Number of total and active sites you can use to get the number of sites in this tenant in the provided time range.
To integrate with Power BI, you can use the Microsoft 365 usage analytics feature within Power BI, which can also be seen via Microsoft 365 admin center > Reports > Usage
.
Here is another article you can read for introduction: Using Power BI for SharePoint Analytics.