I'm trying to forget an SSID from a new Raspberry Pi 4. I need to get it connected to a hidden network in our house, but it grabbed a public guest network first by default, and now I can't get it to go away. I turn off the wifi, edit /etc/wpa_supplicant/wpa_supplicant.conf (yes, as sudo) to remove the existing network reference. Save it, close it, re-open it to confirm that the network has been removed. Turn on wifi, it immediately grabs the same wifi name and reinserts the entry back into wpa_supplicant.
If I erase bad_public from wpa_supplicant and put in good_hidden SSID, it still won't grab it--defaults to bad_public and inserts the record. It sure seems like there's some other place where the record is getting cached and it keeps reconnecting. Thanks for your help.
EDIT to add: Running Raspbian from NOOBS 3.3.1