Just discovered some other VPN applications while there has some errors as well:
- LimeVPN (How to Setup VPN connection in Kubuntu / KDE Plasma using L2TP protocol? | LimeVPN Help Center and LimeVPN Review & Test 2021 - Keep This in Mind Before Buying)
- wireguard (Installation - WireGuard) recently
- install Android VPN apps via Anbox (anbox/install.md at master 路 anbox/anbox 路 GitHub)
Source: https://forum.linuxconfig.org/t/psiphon3-for-linux-os/6377/3?u=englianhu