So I figured out how the invisible walls work (it really wasn't that inobvious, it's just in a jam context I tend tot hink "this is a bug" before I think "these walls are delbieratlety invisible". Got past that screen and made it past the skull screen.... but then I was out of flashes, there was no 'flash reloady' thing like on the seocnd screen and restarting did not restore my flashes. No idea if this is an actual bug or just another instance where I can't figure how I'm supposed to proceed.
Viewing post in The Darkness Remembers jam comments
My number one recommendaiton would be, if you can, calibrate brightness at game start. normally, I find the "adjust brightness until the center image is barely visible" step annoying boilerplate, but I think for a game like this, it's essential. On the level in quesiton, for instance, I could see absolutely nothing without flashes, no box, no button, just pitch blackness, on my monitor anyway. But your game's vibes are still pretty much immaculate, IMHO, which counts for a lot.