Faults with iPhone 12

Do you have Accessibility features (such as Back Tap) turned on? When enabled, these features are shortcuts that perform action, such as starting a recording or taking a photo.

See https://support.apple.com/guide/iphone/back-tap-iphaa57e7885/15.0/ios/15.0.

Does it seem like someone is randomly moving the touchscreen? That can do all sorts of things, including starting apps, deleting icons, entering the passcode, opening the camera, etc.

If that's the case, many call it "ghost touch" and that's usually a failing digitizer, which Apple would only fix via a replacement of the front screen assembly. But there are other causes which may not be fixable by Apple (would require a full replacement). Occasional a software fault, but that's rare.

An Apple diagnostic might trace what the issue is.