macOS AirPlay Receiver now listens on port 5000 by default, which conflicts with the default port used by some frameworks (like Flask). This may cause some confusion if you’re trying to forward port 5000 from a different VM machine and you don’t see anything in your browser.

To fix it, you need to uncheck the option in System Preferences -> Sharing -> AirPlay Receiver. Then it works again, otherwise, if you try to make something listen on port 5000 it may not work