Did you have problems using openfortivpn?
You can install it with:
sudo apt install openfortivpn
then run it from the terminal with:
sudo openfortivpn <host>:<port> -u<username>
https://askubuntu.com/questions/1248538/how-to-install-and-set-up-forticlient-ipsec-vpn-in-ubuntu-20-04