"unexpected keyword arg" when initializing my subclasses

[Gribouillis]

why I shouldn't inherit from that Base-Class?

Metaclasses are for metaprogramming. You don't need that for your first class, so remove the metaclass.

Private attributes with double underscores are more an annoyance than anything else. In Python there is no compiler to enforce more or less privacy on members, so privacy is usually a gentlemen's agreement between the programmer and his/her colleagues. To indicate that an attribute is not in the object's public interface, use a single underscore.

You could write the code this way for example

class MyBaseClass:

    def __init__(self,
                 material=None,
                 origin=None,
                 manufacturer=None,
                 ) -> None:

        self._material = material
        self._origin = origin
        self._manufacturer = manufacturer

class MyClass1(MyBaseClass):
    def __init__(self,
                 name=None,
                 length=None,
                 height=None,
                 color=None,
                 **kwargs,
                 ) -> None:

        super().__init__(**kwargs)

        self._name = name
        self._length = length
        self._height = height
        self._color = color


class MyClass2(MyBaseClass):
    def __init__(self,
                 name=None,
                 vol=None,
                 weight=None,
                 dense=None,
                 **kwargs,
                 ) -> None:

        super().__init__(**kwargs)

        self._name = name
        self._vol = vol
        self._weight = weight
        self._dense = dense

k1 = MyClass1(name='name',
              length='leng',
              height='heig',
              color='colo',
              material='mate',
              origin='orig',
              manufacturer='manu',
            )
print(k1)
print(vars(k1))

Output:
<__main__.MyClass1 object at 0x7fd271dd3ee0>
{'_material': 'mate', '_origin': 'orig', '_manufacturer': 'manu', '_name': 'name', '_length': 'leng', '_height': 'heig', '_color': 'colo'}