I’m certain its hardware (specifically the display); when the Picade first is switched on, I’m used to seeing “HDMI” at the top left for a second or two - even this now appears as blurry vertical lines.
If I try to move the EmulationStation selections left and right using the joystick, I can see the images “moving” across the screen - just obviously very corrupted.
It looks similar to the issue raised here - the difference for me is that the display’s been working fine until today.