Yeah, even in that video… He has the Airframe selected to the A320Neo FBW… That’s why he can pick the Passengers, Cargo, and ZFW from the list.
If you haven’t added the A320Neo Fly By Wire Airframe, before. You can do so by clicking this link.
SimBrief A20N Airframe with the correct weights.
By clicking that link, you should be able to Save that Airframe into your list, and you can pick the aircraft from the list when you generate the flight plan.