I am not sure what your target is. The video is about HA, so I assume you have that diagram.
If you are in designing phase of the network, see to finish the design, you might have to revise it again.
If you use the switch you will probably want to use VLANs (defined on FortiGate network config) and add the VLANs to the switch port (applied on the FortiGate, switch controller port config).
If you want to use the physical ports, you don't need VLANs, but you can use VLANs.
Keep in mind that VLANs, once defined on a physical port, are stuck on that port. It is possible, but difficult to move VLAN123 from port1 to port5 on a FortiGate. On the switch it is easy as all VLANs on FortiGate are defined on a single trunk port, the FortiLink. On the switch controller, port config you can switch and change VLANs as you need it.
This is one thing that I learned when designing my network.
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