I changed some from Dict to Mapping since

mytype = Dict[str, str]

def fn(arg: Dict[str, Union[str, int]]):
    pass

fn(key_value_pairs)

this gives

Argument of type "dict[str, str]" cannot be assigned to parameter "arg" of type "Dict[str, str | int]" in function "fn"
"dict[str, str]" is incompatible with "Dict[str, str | int]"
Type parameter "_VT@dict" is invariant, but "str" is not the same as "str | int"
Consider switching from "dict" to "Mapping" which is covariant in the value typePylancereportGeneralTypeIssues