A ctrl-click appears not to react mac-like & not as mentioned in the Affinity Publisher Beta Help: – For instance in the Swatches Pane:
A ctrl-click on a color swatch opens a pulldown color-pane (with noise slider instead the opacity slider in the 'original' color-pane). The same result occurs with an option-click and with a double-click (no key pressed).
Different to this behaviour the Help says:
"ctrl-click the swatch you want to remove and choose Delete Fill from the pop-up menu."
In MacOS usually a ctrl-click = a right-click. This appears not to work in Publisher, different to its Help-Info.