This is no such thing as Guest Protect. There is “Block All Private IP" and “Custom Subnet” and “Block Exception”. Guest Protect is just a name for this group. Talking about Guest Protect helps no one.
As for Block all private IP, the definition in the other Forum post is :“Check this box to deny all connection attempts by private IP addresses.”
I have no idea what this means. Connection attempt by who? By what? To where? Every router client has a private IP as all of us already know. Useless words.
Custom subnet seems to be a VLAN just for this one SSID. Fine.
Block Exception is a mystery to me. Blocking from which subnet? To where?
I dont see where these 3 features do anything for me that can’t be done with VLANs.
This should be simple, easy and trivial. The basic concepts are always simple.