PowerBI actually has some limits on the volume (rows) of data that it can export, but there is a very simple way to export massive datasets from Power BI:
Install DaxStudio from here https://daxstudio.org/
Open your PowerBI dashboard that is connected to Deep Space (refresh your data from Deep Space cloud if necessary)
Open DaxStudio
Connect to the relevant PowerBI datasource
In the text area, type EVALUATE followed by the table name you would like to Export to raw data
Click the Output button, and choose File
Click Run, and then set your desired filename and export data structure
Your data is now exported to file - even if the data export size would have exceeded the built-in Power BI limits on data exports