Watermelon Ok, now I am at risk of pulling a muscle in my neck from holding my phone above my head and looking at the screen.
I have been able to reproduce that some patterns of flipping the phone face-down, perhaps when also moving it downward as if toward a surface, cause the screen to blank -- in Vanadium, the built-in Clock app, and in Settings. But, for me so far, this does not lock the device. If I flip it back up, or tap the screen twice, etc., then the screen is not locked. This is with my screen timeout set to two minutes.