Hello,
Unfortunately, I cannot provide you with details on how to configure Fortigate with current WebUI. You can check this configuration example with updated Fortigate interface, however, I assume, it might be dated too.
As for configuration of Teltonika device, current WebUI contains all of the same configurable settings except for Identifier type option. For more details on IPsec config check the following link: https://wiki.teltonika-networks.com/view/RUT955_VPN#IPsec
Best regards,