Done that. Thank you.

It should be possible to configure VLANs on the router itself using untagged ports and with their own DHCP assigned IP ranges.

@Metis Got a quick answer from their support team. This router accepts untagged native VLAN in all ports. Other VLANs are passed in tagged mode only. This means that if this router only makes sense...

Just bought this router after all the great specs and promises just to be let down. The list of feature is amazing, but I should know better. Already purchased a couple of VPN routers some time ago...