Hello Nicolas
I think there may be confusion as far as what we mean when we say hub-and-spoke.
The default behavior of an SD-WAN topology is full mesh. This means that all sites can communicate with each other directly. The hub and spoke topology that Rene mentioned in the lab refers to the restriction of allowing each vEdge to communicate ONLY with the central site, and not communicate with any other vEdge device. This is not to be confused with hub and spoke topologies such as DMVPN for example.
What you are suggesting is a third option of operation, which is to force the SD-WAN topology to function as a hub-and-spoke topology and have all communication between sites routed through the hub site rather than directly between vEdge devices, correct? Kind of like a DMVPN Phase 1 situation.
You can direct traffic within the SD-WAN topology to force it to behave in a hub-and-spoke manner using various methods including the VPN topology configuration, routing, data policies, as well as policies that manipulate OMP route advertisement to influence the SD-WAN overlay. SD-WAN was not designed for this, but it can be done. What method you choose really depends upon what you want to achieve.
The question I have however is why would you want to do this? The purpose of this particular lesson is to restrict communication between vEdge devices, not to actually create a hub and spoke topology where traffic is routed through the hub. If you can answer the why, then we can then move on to further discuss the appropriate solution.
I hope this has been helpful!
Laz