You don't see + Addnetwork
Nope, I didn't then but after a cold boot I now do, but the security options are blacked out but it let me enter the SSID and I entered the password without defining the encryption protocol and it connected. It is a no-Internet network.
It asked me to turn off airplane mode before allowing the SSID. I had deleted (forget) the internet wifi prior to trying to add the local. Maybe confused it and hard reset sorted it out. But it should work while in airplane mode -- no? The old 4a has done so for many years.
Ahhh, if only I had bought the 4a-5G back then. ;)