In python is it possible to test if an object is an instance of a subclass of MyClass but not an instance of MyClass?

Question

I want to test if an object is an instance of a subclass but not an instance of the parent class. Example:

class MyClass():
  pass

class Sub1(MyClass):
  pass

class Sub2(MyClass):
  pass

obj = Sub1()
assert isinstance(obj, Sub1 | Sub2) and not isinstance(obj, MyClass)

Is there a test that scales for the case of many subclasses and is less cumbersome than isinstance(obj, Sub1 | Sub2 | ... | SubN).

issubclass(type(obj), MyClass) is compact, but does not exclude objects that are instances of MyClass because a class is considered a subclass of itself.