Shared via mypy Playground

main.py

from typing import Callable, Generic, TypeVarTuple, Unpack

# side note: something like this syntax seems unsupported
# class Class[*Ts=Unpack[tuple[()]]]]:

Ts = TypeVarTuple("Ts", default=Unpack[tuple[()]])
class Class(Generic[*Ts]):
    def foo(self, x: Callable[[*Ts], None]) -> None: ...

def x_no_args() -> None: ...

# works as expected
Class().foo(x_no_args)

# fails
obj: Class = Class()
obj.foo(x_no_args)

# also fails
class Other:
    obj: Class
Other().obj.foo(x_no_args)