Update CSV/Excel instead of overwrite

Hello - this scenario could be easily handled with Power Automate (low/no code).  You can use one of the ready-made templates to move a copy of the file to a different location each day and use Power BI to combine the files from the new location. 

I have included a link to just one of the Power Automate templates available.  There are many others that you can use if your source and destination are different that OneDrive/Sharepoint.

Copy files between OneDrive for Business and SharePoint

https://powerautomate.microsoft.com/en-US/templates/details/958c5ff20efb407e8f22c0568fe1298e/copy-files-between-onedrive-for-business-and-sharepoint/ 

More flow templates:

https://us.flow.microsoft.com/en-us/templates/ 

Power Query - Combine Files from Folder

https://support.microsoft.com/en-us/office/import-data-from-a-folder-with-multiple-files-power-query-94b8023c-2e66-4f6b-8c78-6a00041c90e4#:~:text=Combine%20and%20Transform%20Data%20To,select%20Combine%20%3E%20Combine%20and%20Load. 

Yes, that is correct.  It is pretty easy to add a date stamp to the end of the file name using Power Automate.

You can create a variable that holds the value of today's date and append that to the end of the file name when it is saved:

Similar questions get asked frequently (see links below) but the answer is that this is not something that Power BI is designed to do. Power BI is intended to read and visualize data, not be a repository for storing your data. A database is a more appropriate tool for that.

Update Power BI historical data daily

Store and "freeze" column data prior refresh

Maintain historical Data