Well I am a bit puzzled by this size drop down menu too, Why can't there be all sizes including print and web standard in the drop down menu ? Why there is only apple or mobile products sizes? For example If am designing and event poster it would be very handy to have quick art board creation for A3 and for A5 or then standard web sizes instead of only mobile devices.
When ever I tried to create a artboard within the document the toolbar drop down selection is limited to apple devices and few other mobile devices. why can't I choose different sizes for example A4, A5 or sizes that are useful for websites? affinity products are not used by designers only to design stuff for apple or just for mobile. Is there any way to add custom artboard size to the dropdown list in dartboard toolbar.