Several years ago I posted a diagram of my home LAN. It's still very much the same.
While that diagram covered the wired network, I didn't mention the wireless network. That diagram showed 3 wired IoT devices: the Insteon Hub, the Obihai terminal, and the Cisco femtocell.
I have replaced the Insteon Hub due to failure, upgraded the Obihai to OBi200, and replaced the Cisco with a new AT&T Cell Booster.
For the wireless IoT devices, I've created a "guest" network using my Asus RT-AC68R.
All of my IoT wireless devices use 2.4GHz so I didn't even enable the 5GHz band.
Notice that the Asus screen says:
The Guest Network provides Internet connection for guests but restricts access to your local network.
What it doesn't say is that the guest network as implemented by the Asus allows access FROM the local network TO the guest network.
So I can view and control my IoT devices from my local network.
I was inspired to write this post by a recent article on Android Central. In that article, they say:
Your home router's guest network is wholly separate from the one you connect your smartphone or computer to. [emphasis mine]
Don't believe everything you read on the Internet.