Hello,
I have experience in developing VPN applications. I created a cross-platform VPN application for Windows/Linux/macOS (C++, Qt), a native Android application (Kotlin, C++), a native iOS application (Swift) and a Chrome extension (JS, Vue). The desktop and Android support OpenVPN by using the OpenVPN3 library. The iOS application supports IKEv2. The Chrome extension supports HTTP/HTTPS/SOCKS5 proxies.
From my experience, each platform will require at least two weeks.
Please contact me if you have any questions.
I am looking forward to your reply.