Deploy new fortigate

Have you checked FortiConverter?

Yes, Fortinet's FortiConverter service can be used to migrate a configuration from an older FortiGate device to a new FortiGate NGFW version: 

FortiConverter Service

This service can automatically translate a firewall configuration file from an existing FortiGate device to a new FortiGate model. It can be used directly from the FortiGate GUI or through the FortiConverter portal.

Refer this FAQ for more details on FortiConverter Service.

https://docs.fortinet.com/document/forticonverter-service/23.1.0/online-help/933819/general-faqs

https://community.fortinet.com/t5/FortiGate/Technical-Tip-How-to-load-convert-a-FortiGate-configuration-file/ta-p/197247

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