you would need to use FortiAnalyzer or FortiGate Cloud subscription to get customized reports.
You can get a general report (basically an overview with information about top users, events, web usage etc) using the FortiGate Cloud trial version. FortiGate itself has very limited reporting function - if you have a model with a disk, you should be able to generate similar generalized reports, but there are no filtering/customization options.
To get a specific, filtered report (only VPN users, and only traffic to/from local VLANs) does require either FortiAnalyzer or FortiGate Cloud subscription. If you have your own logging/reporting solution, FortiGate CAN send the raw logs via syslog for example.
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