White spots on my MacBook screen, mostly on light backgrounds

Take a screenshot and look at it on another device. If the spots aren't in the screenshot it's the panel, not software, so no setting will fix it. Bright spots that only show on white backgrounds are usually pressure marks on the backlight layer, from the lid being closed on something or the bag getting squashed. Mine got one like that after a while in a tight backpack. It doesn't normally spread, but the only real fix is a display replacement, which is pricey on a MacBook, so check if you're still under warranty or AppleCare before paying for it.