Hi Rodrigo, in that case you create a new VLAN for that isolated VLAN and create the PortGroup for that isolated VLAN.
Do not create a gateway/interface VLAN/SVI on the physical switch/router.
If you need multiple isolated VLAN and they need to be able to reach each other then you can either use VRF (Virtual routing and forwarding) or use Private VLAN (Private VLAN)