How to hint homogenous list of instances of same subclass?

class A:
   pass 

class A1(A):
   pass

class A2(A):
   pass

def help_here(s: WHAT_SHOULD_I_TYPE_HERE ):
   # How to hint this function that accepts list,
   # where all elements should be instances of same subclass of A.
   # Example 1: [A1(), A1(), A1()] - good
   #            all components all elements are same class,
   #            and it is subclass of A
   # Example 2: [A2(), A2(), A2(), A2()] - valid. Same reason.
   # Example 3: [A1(), A1(), A2()] - invalid, not same classes.
   # Example 4: [1, 2] - invalid. Same class, but not subclass of A.

   if isinstance(s[0], A1):
       # If I use Union[List[A1], List[A2]] as type hint,
       # next line will have no warnings.
       # But if where will be List[A] then warning arrives:
       # Expected type 'List[A1]', got 'List[A]' instead.
       # It's Pycharm IDE.
       process_a1_list(s)


def process_a1_list(lst: List[A1]):
    pass


def another_test():
    # This is just to see, whether IDE will show warnings or not:

    # No warning should be on this block
    good_list: List[A1] = []
    help_here(good_list)
    
    # On both next calls IDE should warn 
    bad_list_1: List[A] = []
    help_here(bad_list_1)

    bad_list_2: List[int] = []
    help_here(bad_list_2)

The only idea I have is: Union[List[A1], List[A2]].

But what if I don't know all subclasses of A?

Are there any beautiful way to hint it?

Update: Not beautiful, but let IDE (Pycharm) check types the way I want.

Update2: I need IDE type hinting solution not Runtime check. I am not sure that solution I want exists at all.

Python 3.8