Unless I’m overlooking it, there doesn’t seem to be a way to preview chords at all in the top section without clicking on the main area which adds it to the progression and replaces a selected chord.
The actual chord names directly underneath are purely descriptive, and would be far more useful if that area was used to trigger chords without adding them.
i.e. Clicking on the letter E previews a the chord, and clicking on the blue V box inserts it as normal