After the last kde/plasma update (arch linux), the file chooser for Storage (Choose a disk file...) no longer accepts any mouse input. This started happening with vbox 6.1.12 and now with the latest 6.1.16. Navigation and selection can only be achieved by physically entering the path and/or file name directly into the Name box. Open and Cancel are also unselectable (CR for open and close window for Cancel). I can find no errors in the system log files that correlate to this.
This applies to plasma 5.20.1; kde 20.08.2.