One of the iPhones on my account (iPhone SE) automatically updated last night even though it was set to “do not auto update”! My iPhone 8 Plus did not auto update. I would suggest if you absolutely do not want Apple to force an auto update, do not plug in your iPhone overnight and do not have it connected to WiFi. That way it will guarantee not to auto update even if Apple has installed a back door to force auto update.
One of the iPhones on my account (iPhone SE) automatically updated last night even though it was set to “do not auto update”! My iPhone 8 Plus did not auto update. I would suggest if you absolutely do not want Apple to force an auto update, do not plug in your iPhone overnight and do not have it connected to WiFi. That way it will guarantee not to auto update even if Apple has installed a back door to force auto update.