Dear Community I want to add more VPN protocols like l2tp, SSL, etc which I installed before in my previous installed system I exactly remember os I install some apps from the software center which has several options for VPNs variety of plugins along with the app SO if anyone knows please help
Most of the protocols you want to install are recognized by your system, but have to be utilized by the vpn connection in order to be used. Sha256 and sha512 are standard as well as TSL, SSL, SSH and PSK... ALL standards of a secure connection. If they offer something specific that your system doesn't have, it is usually installed in their software or instructions for the protocol installation is provided. Proprietary secure connection configurations are always included with the software (i.e. Cisco).
I'm not sure what you're asking to install? Have you researched network security protocols? While some may be discussed, realize older protocols may be depracated for newer, more secure protocols. (IPSEC for L2TP and such). Try reading up on it a little. If you don't understand something, ask.
I Understand but I discover an app on the store which linked with addons like ( SSL,l2pt, PPTP, and cisco ) options are available if you check it whatever you choose then it is automatically added to your gnome network setting with them
I Installed it before renewing my OS that's why I lost in my timeshift snapshot
Using the openvpn config file, that most VPNs offer, lists the protocols needed to use the connection. Nothing is installed, because the protocols exist on the machine already, built into the network service. This is why for most VPNs you don't need to install their software to setup and use it for the connection. Any proprietary protocols would be in their application. Even they are based on the base protocols offered in every network service. Their modifications are usually a custom encryption added to existing protocols or required minimums of the existing protocols. There is no place to download network security protocols for users... it's already built in. Use a VPN that utilizes the protocols you want to enable. If the VPN doesn't support the protocols you are interested in, use a different VPN.
What you are talking about is OpenVPN, which is built in to most Linux distros. What they don't always include is a GUI to manage it. It isn't necessary since the only configuration absolutely necessary is to open network settings, create avpn connection, add the config file to be used and save. There isn't anything more to it than that. You could configure it manually, but if you don't know what protocols are supported by the VPN, you're shooting in the dark.