from typing import Generic, TypeVar, Mapping
T = TypeVar("T")
T2 = TypeVar("T2")

class A(dict[T, T2]):
    ...

def foo(**i: float) -> None:
    ...

a: A[str, str]
d = {"a": "b"}

foo(**a)  # no error
foo(**d)  # error: Argument 1 to "foo" has incompatible type "**Dict[str, str]"; expected "float"