"Word spacing" works in "Align left", "Align right", and "Center", but not in "Full justify".
In the Text or Properties docker, on the Paragraph tab (which is where I believe you adjust the word spacing?), there is a symbol with three dots (cog wheel in later versions) next to the adjustment icons.There you will find the justification spacing settings.Increase the "Min word spacing:" setting to a value that is higher than your desired word spacing, and you will see how the text changes.
Ronny, thank you. That is the solution.