. https://protonvpn.com/blog/openvpn-ios/

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PROTONVPN IOS APP NOW SUPPORTS THE OPENVPN PROTOCOL
Your ProtonVPN iOS app is now better equipped to fight censorship and offers more flexible connection options with the launch of OpenVPN for iOS. The OpenVPN protocol is one of the best VPN protocols because of its flexibility, security, and because it is more resistant to blocks. You now have the option to switch between the faster IKEv2 protocol and the more stable and censorship-resistant OpenVPN protocol. BEN WOLFORD READ MORE