It seems impossible to see the placeholder for the <Number /> input element.
Whenever initialValue/defaultValue props are passed 0, null, undefined or even "" values the value="0" HTML attribute is always rendered.
The only solution for displaying the placeholder is passing value="" prop, but obviously the prop doesn't use the built-in onChange handling then and becomes non-editable.
<Number
name="somename"
placeholder={"Test placeholder"}
/>