[Python] Mypy issue with generics and overload

I'm trying to add types to my code and now have problem. Below is minimal version of code. I cant take a point why B[str] | B[bytes] is incompatible with A[T]. Two last errors is also unexcepted for me (but they will be fixed if change signature .get_object(...) -> A[T]

Why my solution is wrong and what should I change?

from abc import abstractmethod
from typing import TypeVar, overload, Generic, Literal

T = TypeVar('T', str, bytes)
class A(Generic[T]):
pass

class B(A[T]):
def __init__(self, x: T) -> None:
self.x: T = x

class C(A[bytes]):
def __init__(self, x: bytes) -> None:
self.x: bytes = x

class AbstractCreator:
@abstractmethod
def get_object(self, x: Literal["bytes", "str"]) -> A[T]:
...

class BCreator(AbstractCreator):
@overload
def get_object(self, x: Literal["bytes"]) -> B[bytes]:
...

@overload
def get_object(self, x: Literal["str"]) -> B[str]:
...

def get_object(self, x: Literal["bytes", "str"]) -> A[T]:
if x == "bytes":
return B(b"test")
if x == "str":
return B("test")


but mypy get an error

main.py:22: error: Signature of "get_object" incompatible with supertype "AbstractCreator" [override]
main.py:22: note: Superclass:
main.py:22: note: def [T: (str, bytes)] get_object(self, x: Literal['bytes', 'str']) -> A[T]
main.py:22: note: Subclass:
main.py:22: note: @overload
main.py:22: note: def get_object(self, x: Literal['bytes']) -> B[bytes]
main.py:22: note: @overload
main.py:22: note: def get_object(self, x: Literal['str']) -> B[str]
main.py:32: error: Incompatible return value type (got "B[bytes]", expected "B[str]") [return-value]
main.py:34: error: Incompatible return value type (got "B[str]", expected "B[bytes]") [return-value]

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