That’s a tricky one. There’s lots of components in the cel shader that re-introduce light to a scene and even more that take it away again.
The near/far colour grading values are multipliers, so setting it to 0 will indeed be pitch black. Try a value of between 0 and 1.
A better option might be to remove the lighting from the scene entirely - normally if you want a dark map with dynamic spotlights you’d remove the skylight as this simulates a daylight environment but isn’t so good for indoors/nighttime scenarios. If things you don’t want to be lit are still lighting up, disable the cel shader’s postprocess volume briefly to verify it’s not the cel shader causing it. Also make sure you rebuild your lighting.