What's the white stuff that's on top of the food that's been in the fridge for at least 3 days now?

Probably mold, but depending on what the food is, it could be congealed fat.

It could also be a layer of ice crystals if it was too cold in there.

What is the food? Stew? . Could it be a layer of fat? I’d eat it.
But then again I’d eat anything.

What’s in the pot? What does the white stuff look like? Is it fuzzy, smooth, greasy, solid, liquidy?

It’s a sign not to eat it.

Most likely it’s mold, from the saliva of someone sticking a spoon into the pot and eating whatever it is right out of the pot.

Could 3 or 4 days really be more like 5 or 6 days? Not sure? Don’t eat it.

Fungus.

If you can’t positively identify it, please don’t eat it. Better to go hungry for a while than risk poisoning yourself.

As George Carlin once said, ” Could be meat. Could be cake,”