Starting with FortiOS 7.2.1, Fortinet removed built-in 15 days free evaluation license from the Fortigate VM images. It was replaced with the permanent evaluation license, still free. The steps to get it have changed - you now have to create a free Forticare/FortiCloud account, and use it inside the Fortigate GUI to activate this evaluation license. The license will be generated and added to your Forticloud account automatically.
The Fortinet Security Fabric brings together the concepts of convergence and consolidation to provide comprehensive cybersecurity protection for all users, devices, and applications and across all network edges.