A VPN is a network service that protects user data by changing IP addresses and DNS servers to different locations such as overseas so that data cannot be accessed by outsiders. In other words, a VPN can protect one's online activities.
But according to security researcher Michael Horowitz, VPNs on iOS don't really work and user data is all transmitted outside of the VPN connection.
In iOS, when a VPN is connected all network connections will be closed and will be opened through a special route for a more secure connection. A VPN is supposed to close all insecure connection paths, but on iOS these paths are not allowed to close.
Michael stated that Apple has been aware of this problem for the past two years in iOS 13, and to this day Apple still has not fixed it. ProtonVPN service has been aware of this problem since 2020 and any VPN service on iOS cannot protect user data. he also tested various VPN services on iOS 15.6 and the problem still occurs.
Apple does offer developers a way around this problem, where there is code provided in iOS to fix it – but this feature is not activated automatically. Michael says the safest way to use a VPN on iOS is to use a WiFi connection on a router that has a built-in VPN. This means, if the data connection is mobile – the VPN may not be able to protect the user's data at all.