All IoT devices on my network go into a VLAN that blocks internet access. Using Unifi, I think it's just a checkbox to turn internet access on/off. I use a virtual nic on my Home Assistant VM that recognizes that vlan and can communicate with all those devices, as well as a separate nic which is hooked up to the main vlan.
This is the most ungrateful comment I've read today, harping away about how 'it should have been done'.
Well you fucking do it then.
I know that my time is so short (because I have a family) that if I can even do a project then I'm almost certainly not going to document it because getting it done will be enough of a stretch for me, and if I need to come back and re-do it again, I am probably not going to even bother. Not all of us live in mom's basement and have the luxury of extra time.