It is not sufficent to use the cursor keys only to pick an item. You must also press the space bar once on the desired targets and asterisk the item prior proceeding with OK.
Like I said, I had to *install* dialog...
While I think a CLI is better (dialog doesn't play well with tmux if the dialog doesn't fit the pane), if you insist, a good idea would be to change the message following "OK" if nothing is selected because now you get the impression something happened (apart from a couple of near-empty dirs), and the note about PATH intones that.
But thank you, that was it, it now works.