This code produces no error:

from typing import NamedTuple

class A(type): ...

class Foo(NamedTuple, metaclass=A, x=1):
   x: int
   
   
from enum import Enum

class E(Enum, x=1):
    a = 1

It is much easier with the NamedTuple, but, I think that enum might allow some keywords like boundary=STRICT.

So, I think that I will split the PRs for these two problems.

Refs #16432