If I'm understanding your question, you are able to store data in a SharePoint list or on the backend of a form, save it to OneDrive to manipulate with Excel and then import the Excel into PBI. A similar process could be followed with SQL.

However, I'd recommend performing the functions and manipulations in PBI to reduce the risk and make the process cleaner. Though, I can appreciate the idea of getting the data ready in excel, first, then moving to PBI. When I started with PBI I did that but then forced myself to re-make it all in PBI so I could remove Excel from the process. In the long run, that will be better and introduce less variables.