If you want to block application traffic, which is not showing in application control signature, you can create the signature of your own and then apply it to block the traffic. Kindly check below link for application signature creation:
If the application signature which you are looking to block is not in the list of signatures, you could create a custom signature for the application and block the application. You may refer to this link for the same:
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.