In the interim, the invocation of Floating Citations is a double-tap of the hot key in the ‘other’ app, e.g. Tinderbox. The invoking app’s icon & name are shown at left (see grab above), IOW, if invoked from Word you’d see the MS Word logo, etc. Bookends v13.1.2 must be open for its Floating Citations to be called.
As notes, the default call is shift-shift and this can be changed in the ‘Scan & Bib’ section of Bookends prefs to a double-tap of any of: Shift (default), Control, Command, Option or caps Lock key. Whichever chosen, the shortcut is the same key pressed twice in rapid succession. Easily remembered, once you’ve tried it.
Another nice bit of inter-app polish by Jon at Sonnysoftware (Bookends), no doubt with co-operation of some other apps’ devs too.