This would simply do it?

from typing import Dict, Union, Set

RecordType = Dict[Union[int, str], Set[str]]


def my_func(rec: RecordType):
    pass


my_func({1: {'2'}})
my_func({1: {2}})

This code will generate a warning from your IDE on the second call to my_func, but not on the first. As @sahasrara62 indicated, more here https://docs.python.org/3/library/stdtypes.html#types-genericalias

In case users look for a distinct nominal typedef:

from typing import Dict, Union, Set, NewType

RecordType = Dict[Union[int, str], Set[str]]
DistinctRecordType = NewType("DistinctRecordType", Dict[Union[int, str], Set[str]])

def foo(rec: RecordType):
    pass

def bar(rec: DistinctRecordType):
    pass

foo({1: {"2"}})
bar(DistinctRecordType({1: {"2"}}))
bar({1: {"2"}}) # <--- this will cause a type error

This snippet demonstrates that only explicit casting will do.

$ mypy main.py
main.py:14: error: Argument 1 to "bar" has incompatible type "Dict[int, Set[str]]"; expected "DistinctRecordType"
Found 1 error in 1 file (checked 1 source file)