So I have this recently-bought router from TP-Link which replaced an old Asus router that wasn’t cutting it anymore. Anyways, it has the ability to create a separate “IoT Network” for connected appliances/devices.
But it isn’t a separate network. It’s just another SSID with potentially weaker security. Devices can still access both the internet and your local machines. It is totally useless security theater.
Oh, and if I want to isolate any of my “smart” devices from the wider internet while still letting things on the LAN connect to them? I can’t! There is literally no way to do this within the router, except via a really hacky workaround where I add a device as one of my “children” and then use parental controls to restrict Internet usage to one minute per day. (Zero minutes per day is not allowed.)
Not that it matters, because my smart TV locked up if on a network but not on the internet. So I lobotomized it via factory reset. As a dumb TV it works great.

