This is an example only for Android.
I use free OpenVPN configuration file from this site VPN Gate. I am not sure how long it will work with the free ovpn file. It's better to update ovpn files with your own ovpn.
Note that OpenVPN may always wait for the server to respond due to your network.
You can also try to use docker-openvpn or openvpn-install to deploy a VPN service locally.
yarn
yarn android