A screenshot of the file selection dialog might help. I suspect that the window pane showing the list of files is not expanded. You should see on the right side about midway between top and bottom a small area to use for grabbing/selecting - click and drag it to expand the list.
The dialog is Qt's file dialog and was chosen because the native dialog didn't behave well with the progress dialog. It may be different now under Qt5 so I'll test it.