For LCD screens it doesn’t matter. They use the same amount of power whether the screen is black or white. There’s no way to damage the screen by displaying an image.
OLED displays are vulnerable to burn in. So a bright static image left on screen for a long time can result in a latent image that’s permanently burned into the screen. That’s because the OLEDs degrade faster when they’re brighter. But a black screen should have no effect.
Where they banned in all their various applications? Because I had a scare when my 2-year-old granddaughter found a box with a magnetic latch and the magnet had been torn out. We thought she ate it. But after scouring the area we found it, and it’s a thin neodymium magnet. Went through the whole house making sure boxes like that were out of her reach.
Sounds like your SD card is defective. Try a new card.
Not as tough as it seems. People routinely memorize much more in shorter periods. Try learning the complete Kanji (Asian Pictograms) or heiroglyphics. It’s not inconceivable to memorize 10,000 random words. Think of how many songs you can recite the lyrics to. I learned Billy Joel’s, “We Didn’t Start the Fire” in a day. That’s pretty much what this challenge is about - a random list of words.
Gas bubbles from rotting vegetation are the likely cause in this instance. See this article for an explanation:
You can do all that and more with an off-the-shelf mini PC running Linux. No need to reinvent a general purpose computer from a router. The chain of trust thing is above my paygrade, but I bet something like that exists.