Skimming that post shows a lot of people saying that first layer doesn’t affect top layer. What is your definition of z height? We may have a definition issue on our hands here. To me, it means the distance between the nozzle and the bed on the first layer.
I’d be with you on the underextrusion though if the very top layer didn’t look so good. I would bet OP doesn’t have enough layers on top of the infill leading to an artifact that resembles underextrusion.
Sure, on the first layer. We can’t see the first layer here, only the top layer, so it can’t be the z height.
What kind of Ender 3 is it? I flashed mine when I swapped to the silent mainboard. If you can figure out what kind of board you have, and any accessories that plug into the board, you should be able to narrow it down quite a bit.
How can you tell that OP hasn’t leveled their bed properly? You can’t see the bottom layer in their picture.
I’ve fixed blue screens by flashing the correct firmware. Have you given that a try?
I’m not OP, but I would guess they cut out one dinosaur profile and wanted another to match. The copying guide allowed them to set the first cutout on top of another sheet of plywood and then trace around the template. You can see a sleeve around the router bit that would protect whatever the router is sitting on.