When you say clean up, what do you mean? Delete?

I'd have the user delete it, not you.



We are just moving to OneDrive and have users move stuff from their private drive U:\<username> to one drive.

If things are not moved until a certain date, their U:\ drive will get deleted with the assumption that the stuff is no longer needed. ¯\_(ツ)_/¯



But after the retention period and the user still not made a change, you can use Powershell for example to find files and folder older than X days or months or whatever and have it delete or move them.