White dots appearing on my laptop screen

Bright white spots that only show on dark backgrounds are usually pressure marks rather than dead pixels. Dead pixels stay black, stuck ones show a single colour. The white blotches come from the backlight layer behind the panel getting pressed, often by the keyboard or something in the bag pressing the lid while it's shut. They don't spread by themselves, but more pressure makes more of them. Keep the bag free of chargers on the screen side and avoid closing it on anything. Fixing existing ones means a new panel, so most people just live with them.