If you're doing casting its probably a code smell and good indicator of something being off, or you're doing something too exotic. I'd say this applies a good amount to normal compiled languages too.

To do types well, I'd recommend constraining as much as possible. E.g. if a library gives you a union of 5 possible return types, just type it as one of them that you know you'll get and don't let that "complexity" propagate further into your code base. Likewise if you're wrapping a lib function that can take 3 levels worth of complex union or umpteen varargs, don't let that bleed through in your function signature "just in case".

And most crucial advice. Don't use Google's type checker pytypes. Or any other type checker for that matter other than Pycharms built-in one and mypy. Don't faff about with vscode either. Pycharm will make your python type hinting journey a pleasant experience (barring some generics and OOP corner case scenarios.)