Quantity is an observation.
To assign a quantity to nothing is an abstraction.
Which is why there were some cultures that had numbers but did not have zero.
They could see, but they could not abstract.
The idea of a 'coin' or 'money' and so on is abstract, but the object itself, shape, mass, composition, etc, is objective.
Who said anything of the coin object not being objective?
Thing is: objects are abstractions. Not what the object abstsction represents, thst is something real, but the abstraction of som part of reslity being an object.