There are actually two signatures:

EnumCls(value) --> return member with value `value`

EnumCls(name, members, module, qualname, type, start) --> create new Enum

An example of the first:

class A(Enum):
    x = 1
A(1) --> <A.x: 1>

an example of the second:

class A(Enum):
    pass
B = A('B', {'y':2})
B(2) --> <B.y: 2>

The reason for the error you see is that Enums with members cannot be further subclassed.