When I run the command
apt-cache search network-manager | grep sstp
It comes up blank. I can find pptp and openvpn, but not sstp.
Have the relevant sstp packages been removed?
[edit] - This worked for me
I ran the commands below
sudo add-apt-repository ppa:eivnaes/network-manager-sstp
sudo apt-get update
sudo apt-get install network-manager-sstp
sudo apt-get install sstp-client
I then opened network connections with
nm-connection-editor
and I was able to set up a VPN from there.