Disable upside down rotation My phone should have rotation completely disabled - i.e. "Auto-Rotate" icon in fast settings pulldown is grey, "Settings->Display->When device is rotated" says "Stay in portrait view", "Settings->Accessibility->Auto-rotate screen" is off. Actually they seem like shortcut to a same single setting, because they all change simultaneously when I change any of them.

Despite all that, when I turn the phone upside down or when vibration makes it think that it was turned upside down, image rotates upside down too.

It is extremely distracting, as I never actually do it myself - it would be uncomfortable to use hardware buttons - but pretty much any vibration in application makes phone think that it was turned for a moment. I always have to shake it a few times to make it turn back afterwards. Disabling vibration is not an option because it is used for important alerts and I often use have volume down or use phone in noisy environment.

Is there a way to completely disable this rotation?
Use apps like Ultimate Rotation Control - with proper settings, it seamlessly integrates with system rotation toggle, and on top of that you can disable any rotation direction you don't want (most phones don't have upside-down rotation, have to be enabled this way), force apps that don't usually rotate to rotate, and set per-app rotation behavior. In your case, just select "Forced 3/4 Auto" and "Lock Current" in rotation choices.