Try this, maybe it's function is unabled.
Choose setting for USB connection
Slide your finger downwards starting from the top of the screen. Press the connection icon. Press Transfer files to turn on the function.
You just have to uninstall the driver from the Pc, by going to:SpaceDesk lets me use the phone as an external monitor over USB cable. once i found out it cant transfer files, i uninstalled the app.
now, even without the app, i cant transfer files as seen here:any idea how i can resolve???