I read somewhere that a guest account only accesses the 2.4 ghz band when created?
Since I am trying to setup home automation devices, this would be handy since Google puts everything on 5 ghz if possible, like the phone trying to setup the automation!
But I can't find any reference or documentation for this?
The guest WiFi network supports both 2.4GHz and 5GHz clients just like the primary network. Setting up most 2.4GHz-only devices isn't a problem in most cases. However, there are a few poorly designed devices that have trouble with mixed 2.4GHz/5GHz networks that are increasingly common. There are a few methods to make these devices work, but none are fantastic. The simplest is to walk far enough away to force your phone off of 5GHz and onto 2.4GHz during the setup procedure. You shouldn't need to bring the IoT device with you for that, though you may need a helper.