How do I stop a specific WiFi network from turning on WiFi automatically in Oreo
So, if the WiFi turned on automatically and is connecting to the network, you need to turn the WiFi off.
When I did that, I got the following notification:


  Turn on Wi-Fi automatically
  "[SSID]" has been removed from your frequently used Wi-Fi networks.
  It will be added again if you use it more often.


Apparently that is enough to remove it temporarily at least. No idea how long it takes until it is added again.