Cannot split bands

I am trying to set up my new Xfinity wifi - I have a Gateway XB8. I have MANY home devices that need a 2.4 ghz band. I've been looking online for > 1 hour for how to do this, but nothing works. The admin webpage (10.0.01) says I need to go to the app, so this webpage seems disabled at least for new gateways. On the app, I go to "wifi equipment" then "advanced settings" as directed on other websites, but there is no option to split the bands (as some websites say). When I go to "WiFi details" then "Edit Wifi Settings" there is no option to split the bands to 2.4, 5, and 6 - as other websites say. I think I need to specifically have a 2.4 ghz band for the MANY devices (plugs, lights, fans, etc...) that require it. Can anyone help? I'm at a loss.