How to create a VPN connection to a FortiGate Firewall in Ubuntu 18.04 Linux

how do I setup and create a SSL-VPN-tunnel using Ubuntu 18.04 Linux?

I downloaded the Forticlient.

On Windows I see a “REMOTE ACCESS” option on the left side of the client.

However on Ubuntu 18.04 Linux I do not see the same menu:

So how do I setup and create a SSL-VPN-tunnel using Ubuntu 18.04 Linux?

Most of the Fortinet knowledge base pages are mostly blank: Tested with Firefox and Chromium.

Also is it possible with standard linux tools to connect or must I use the FortiGate Forticlient to connect?

The remote access is currently not available in Forticlient 6.0 for Linux. You can see the official compatibility chart when you scroll down in the following link: Forticlient compatibility

You can use the openfortivpn client: Installing openfortivpn

FortiClient 6.2, Fabric Agent with Endpoint Protection and Cloud Sandbox, can be purchased and the Linux version supports SSL VPN: FortiClient 6.2 Compatibility

Here is Forticlient – SSLVPN app we use at my work as an alternative to FortiClient for linux users.

The interface is very similar to forticlient:

^{much better alternative if you ask me, as it does not silently install antivirus bloatware ;)}