VoiceOver turns on by itself on iphone12
My iphone was turning itself on at random times and I had no idea why. I think I discovered why this was happening and wanted to share with others. After VoiceOver off with Siri, I went to Settings -> Accessibility -> Touch -> Back Tap (presumably tapping the back of the phone?) -> Double Tap -> My phone was set to "VoiceOver". I changed it to "None". To change it back (which I NEVER want to do) the alternative option to "None" is "Accessibility Shortcut" which can be set to several options, including VoiceOver. Hope this helps!
iPhone 5c, iOS 10