I much appreciate the addition of 'Data files' to Calibre, though I find adding files to it is a bit cumbersome:
right-click on title -> hover over 'Edit metadata' -> move to 'Manage data files' -> click 'Add files' -> navigate to where you have your file(s) and add.
Any chance we could get a
drag & drop - at least to the 'Manage data files' pop-up window?
Cheers and congrats (as usual) to a wonderful app!