Fritzbox Wireguard and Linux Mint

Firstly, you need to install Wireguard. Then comes the building of the GUI  from source code. Here are the steps.

cd ~/
sudo apt install wireguard git dh-autoreconf libglib2.0-dev intltool build-essential libgtk-3-dev libnma-dev libsecret-1-dev network-manager-dev resolvconf

git clone https://github.com/max-moser/network-manager-wireguard
cd network-manager-wireguard
./autogen.sh --without-libnm-glib

./configure --without-libnm-glib --prefix=/usr --sysconfdir=/etc --libdir=/usr/lib/x86_64-linux-gnu --libexecdir=/usr/lib/NetworkManager --localstatedir=/var

make
sudo make install

Once the building completes successfully, you should be able to see the Wireguard VPN option in the Network Manager settings (Settings -> Network ->VPN) .

When you want to uninsytall  wireguard, just go into the directory network-manager-wireguard with a terminal and run :

sudo make uninstall